SERVER-74787 Prepare jstest corpus for implicit strict mode

author: Matt Broadstone <mbroadst@mongodb.com> 2023-05-07 16:15:25 +0000
committer: Evergreen Agent <no-reply@evergreen.mongodb.com> 2023-05-07 16:55:23 +0000
commit: 43b87324302209cbfa240d6c6b520007669e4ea6 (patch)
tree: 7039a07f7116ad86df64fd21eee62f84053ba92e /jstests/core
parent: 948bf37c910d9911160e3b275d3c51b146a9c923 (diff)
download: mongo-43b87324302209cbfa240d6c6b520007669e4ea6.tar.gz
429 files changed, 1112 insertions, 1372 deletions
diff --git a/jstests/core/administrative/auth1.js b/jstests/core/administrative/auth1.js
index 7633644c0da..4b41c7e21bb 100644
--- a/jstests/core/administrative/auth1.js
+++ b/jstests/core/administrative/auth1.js
@@ -15,7 +15,7 @@
 var mydb = db.getSiblingDB('auth1_db');
 mydb.dropAllUsers();
 
-pass = "a" + Math.random();
+let pass = "a" + Math.random();
 // print( "password [" + pass + "]" );
 
 mydb.createUser({user: "eliot", pwd: pass, roles: jsTest.basicUserRoles});
@@ -23,7 +23,7 @@ mydb.createUser({user: "eliot", pwd: pass, roles: jsTest.basicUserRoles});
 assert(mydb.auth("eliot", pass), "auth failed");
 assert(!mydb.auth("eliot", pass + "a"), "auth should have failed");
 
-pass2 = "b" + Math.random();
+let pass2 = "b" + Math.random();
 mydb.changeUserPassword("eliot", pass2);
 
 assert(!mydb.auth("eliot", pass), "failed to change password failed");
diff --git a/jstests/core/administrative/auth2.js b/jstests/core/administrative/auth2.js
index eb2b47f696f..4851ac10575 100644
--- a/jstests/core/administrative/auth2.js
+++ b/jstests/core/administrative/auth2.js
@@ -8,7 +8,7 @@
 
 // SERVER-724
 db.runCommand({logout: 1});
-x = db.runCommand({logout: 1});
+let x = db.runCommand({logout: 1});
 assert.eq(1, x.ok, "A");
 
 x = db.logout();
diff --git a/jstests/core/administrative/check_shard_index.js b/jstests/core/administrative/check_shard_index.js
index f6bb9f3ee7a..bf12d6e4417 100644
--- a/jstests/core/administrative/check_shard_index.js
+++ b/jstests/core/administrative/check_shard_index.js
@@ -11,7 +11,7 @@
 //  CHECKSHARDINGINDEX TEST UTILS
 // -------------------------
 
-f = db.jstests_shardingindex;
+let f = db.jstests_shardingindex;
 f.drop();
 
 // -------------------------
@@ -22,7 +22,8 @@ f.drop();
 f.createIndex({x: 1, y: 1});
 assert.eq(0, f.count(), "1. initial count should be zero");
 
-res = db.runCommand({checkShardingIndex: "test.jstests_shardingindex", keyPattern: {x: 1, y: 1}});
+let res =
+    db.runCommand({checkShardingIndex: "test.jstests_shardingindex", keyPattern: {x: 1, y: 1}});
 assert.eq(true, res.ok, "1a");
 
 f.save({x: 1, y: 1});
diff --git a/jstests/core/administrative/getlog1.js b/jstests/core/administrative/getlog1.js
index a5989e87c75..07c623573ef 100644
--- a/jstests/core/administrative/getlog1.js
+++ b/jstests/core/administrative/getlog1.js
@@ -5,7 +5,7 @@
 // to run:
 //   ./mongo jstests/<this-file>
 
-contains = function(arr, obj) {
+let contains = function(arr, obj) {
     var i = arr.length;
     while (i--) {
         if (arr[i] === obj) {
diff --git a/jstests/core/administrative/profile/profile3.js b/jstests/core/administrative/profile/profile3.js
index 68334e72b08..1ab42d62216 100644
--- a/jstests/core/administrative/profile/profile3.js
+++ b/jstests/core/administrative/profile/profile3.js
@@ -14,10 +14,10 @@ var stddb = db;
 var db = db.getSiblingDB("profile3");
 
 db.dropAllUsers();
-t = db.profile3;
+let t = db.profile3;
 t.drop();
 
-profileCursor = function(query) {
+let profileCursor = function(query) {
     print("----");
     query = query || {};
     Object.extend(query, {user: username + "@" + db.getName()});
@@ -25,7 +25,7 @@ profileCursor = function(query) {
 };
 
 try {
-    username = "jstests_profile3_user";
+    var username = "jstests_profile3_user";
     db.createUser({user: username, pwd: "password", roles: jsTest.basicUserRoles});
 
     db.logout();
diff --git a/jstests/core/administrative/set_param1.js b/jstests/core/administrative/set_param1.js
index dfe71da85d2..35eaa68ca44 100644
--- a/jstests/core/administrative/set_param1.js
+++ b/jstests/core/administrative/set_param1.js
@@ -9,6 +9,7 @@
 //   # migration hook.
 //   tenant_migration_incompatible,
 // ]
+load("jstests/libs/fixture_helpers.js");
 
 // Tests for accessing logLevel server parameter using getParameter/setParameter commands
 // and shell helpers.
@@ -165,8 +166,7 @@ assert(!result,
 assert.commandWorked(
     db.adminCommand({"setParameter": 1, redactEncryptedFields: old.redactEncryptedFields}));
 
-const isMongos = (db.hello().msg === 'isdbgrid');
-if (!isMongos) {
+if (!FixtureHelpers.isMongos(db)) {
     //
     // oplogFetcherSteadyStateMaxFetcherRestarts
     //
diff --git a/jstests/core/api/apitest_db.js b/jstests/core/api/apitest_db.js
index 805e2c8f990..a2f29340088 100644
--- a/jstests/core/api/apitest_db.js
+++ b/jstests/core/api/apitest_db.js
@@ -8,7 +8,7 @@
 
 assert("test" == db, "wrong database currently not test");
 
-dd = function(x) {
+let dd = function(x) {
     // print( x );
 };
 
diff --git a/jstests/core/capped/capped.js b/jstests/core/capped/capped.js
index 6c62ba75560..1a26f5a1e22 100644
--- a/jstests/core/capped/capped.js
+++ b/jstests/core/capped/capped.js
@@ -9,7 +9,7 @@
 db.jstests_capped.drop();
 db.createCollection("jstests_capped", {capped: true, size: 30000});
 
-t = db.jstests_capped;
+let t = db.jstests_capped;
 assert.eq(1, t.getIndexes().length, "expected a count of one index for new capped collection");
 
 t.save({x: 1});
diff --git a/jstests/core/capped/capped1.js b/jstests/core/capped/capped1.js
index df9b12ddf89..5a02fb6c55f 100644
--- a/jstests/core/capped/capped1.js
+++ b/jstests/core/capped/capped1.js
@@ -6,11 +6,11 @@
  * ]
  */
 
-t = db.capped1;
+let t = db.capped1;
 t.drop();
 
 db.createCollection("capped1", {capped: true, size: 1024});
-v = t.validate();
+let v = t.validate();
 assert(v.valid, "A : " + tojson(v));  // SERVER-485
 
 t.save({x: 1});
diff --git a/jstests/core/capped/capped5.js b/jstests/core/capped/capped5.js
index a276baf043d..d2b704c6cb9 100644
--- a/jstests/core/capped/capped5.js
+++ b/jstests/core/capped/capped5.js
@@ -6,9 +6,9 @@
  * ]
  */
 
-tn = "capped5";
+let tn = "capped5";
 
-t = db[tn];
+let t = db[tn];
 t.drop();
 
 db.createCollection(tn, {capped: true, size: 1024 * 1024 * 1});
diff --git a/jstests/core/capped/capped_empty.js b/jstests/core/capped/capped_empty.js
index e0515967ca8..020be638c61 100644
--- a/jstests/core/capped/capped_empty.js
+++ b/jstests/core/capped/capped_empty.js
@@ -15,7 +15,7 @@
  * ]
  */
 
-t = db.capped_empty;
+let t = db.capped_empty;
 t.drop();
 
 db.createCollection(t.getName(), {capped: true, size: 100});
diff --git a/jstests/core/capped/cappeda.js b/jstests/core/capped/cappeda.js
index 3ec0074eefe..816f5be4e0d 100644
--- a/jstests/core/capped/cappeda.js
+++ b/jstests/core/capped/cappeda.js
@@ -6,13 +6,13 @@
  * ]
  */
 
-t = db.scan_capped_id;
+let t = db.scan_capped_id;
 t.drop();
 
-x = t.runCommand("create", {capped: true, size: 10000});
+let x = t.runCommand("create", {capped: true, size: 10000});
 assert(x.ok);
 
-for (i = 0; i < 100; i++)
+for (let i = 0; i < 100; i++)
     t.insert({_id: i, x: 1});
 
 function q() {
diff --git a/jstests/core/commands_namespace_parsing.js b/jstests/core/commands_namespace_parsing.js
index d352a0e3576..b48801beef5 100644
--- a/jstests/core/commands_namespace_parsing.js
+++ b/jstests/core/commands_namespace_parsing.js
@@ -19,6 +19,7 @@
 //   does_not_support_causal_consistency,
 //   uses_compact,
 // ]
+load("jstests/libs/fixture_helpers.js");
 
 // This file tests that commands namespace parsing rejects embedded null bytes.
 // Note that for each command, a properly formatted command object must be passed to the helper
@@ -63,9 +64,7 @@ function assertFailsWithInvalidNamespacesForField(
     }
 }
 
-const hello = db.runCommand("hello");
-assert.commandWorked(hello);
-const isMongos = (hello.msg === "isdbgrid");
+const runningOnMongos = FixtureHelpers.isMongos(db);
 
 db.commands_namespace_parsing.drop();
 assert.commandWorked(db.commands_namespace_parsing.insert({a: 1}));
@@ -182,7 +181,7 @@ assertFailsWithInvalidNamespacesForField("collection",
                                          isNotFullyQualified,
                                          isNotAdminCommand);
 
-if (!isMongos) {
+if (!runningOnMongos) {
     // Test godinsert fails with an invalid collection name.
     assertFailsWithInvalidNamespacesForField(
         "godinsert", {godinsert: "", obj: {_id: 1}}, isNotFullyQualified, isNotAdminCommand);
@@ -206,13 +205,13 @@ assertFailsWithInvalidNamespacesForField(
 assertFailsWithInvalidNamespacesForField(
     "planCacheClear", {planCacheClear: ""}, isNotFullyQualified, isNotAdminCommand);
 
-if (!isMongos) {
+if (!runningOnMongos) {
     // Test cleanupOrphaned fails with an invalid collection name.
     assertFailsWithInvalidNamespacesForField(
         "cleanupOrphaned", {cleanupOrphaned: ""}, isFullyQualified, isAdminCommand);
 }
 
-if (isMongos) {
+if (runningOnMongos) {
     // Test enableSharding fails with an invalid database name.
     assertFailsWithInvalidNamespacesForField(
         "enableSharding", {enableSharding: ""}, isNotFullyQualified, isAdminCommand);
@@ -266,7 +265,7 @@ assertFailsWithInvalidNamespacesForField(
 assertFailsWithInvalidNamespacesForField(
     "create", {create: ""}, isNotFullyQualified, isNotAdminCommand);
 
-if (!isMongos) {
+if (!runningOnMongos) {
     // Test cloneCollectionAsCapped fails with an invalid source collection name.
     assertFailsWithInvalidNamespacesForField(
         "cloneCollectionAsCapped",
@@ -308,7 +307,7 @@ assertFailsWithInvalidNamespacesForField(
 assertFailsWithInvalidNamespacesForField(
     "dropIndexes", {dropIndexes: "", index: "*"}, isNotFullyQualified, isNotAdminCommand);
 
-if (!isMongos) {
+if (!runningOnMongos) {
     // Test compact fails with an invalid collection name.
     assertFailsWithInvalidNamespacesForField(
         "compact", {compact: ""}, isNotFullyQualified, isNotAdminCommand);
@@ -322,7 +321,7 @@ assertFailsWithInvalidNamespacesForField(
     isNotAdminCommand);
 
 // Test reIndex fails with an invalid collection name.
-if (!isMongos) {
+if (!runningOnMongos) {
     assertFailsWithInvalidNamespacesForField(
         "reIndex", {reIndex: ""}, isNotFullyQualified, isNotAdminCommand);
 }
diff --git a/jstests/core/commands_with_uuid.js b/jstests/core/commands_with_uuid.js
index b0260e0bc31..3744e038992 100644
--- a/jstests/core/commands_with_uuid.js
+++ b/jstests/core/commands_with_uuid.js
@@ -10,6 +10,7 @@
  *   assumes_no_implicit_index_creation
  * ]
  */
+load("jstests/libs/fixture_helpers.js");
 
 (function() {
 'use strict';
@@ -29,10 +30,7 @@ if (uuid == null) {
 }
 
 // No support for UUIDs on mongos.
-const hello = db.runCommand("hello");
-assert.commandWorked(hello);
-const isMongos = (hello.msg === "isdbgrid");
-if (isMongos) {
+if (FixtureHelpers.isMongos(db)) {
     return;
 }
 
diff --git a/jstests/core/connection_string_validation.js b/jstests/core/connection_string_validation.js
index 6236e445a77..43a7373b973 100644
--- a/jstests/core/connection_string_validation.js
+++ b/jstests/core/connection_string_validation.js
@@ -5,7 +5,7 @@
 // ]
 // Related to SERVER-8030.
 
-port = "27017";
+let port = "27017";
 
 if (db.getMongo().host.indexOf(":") >= 0) {
     var idx = db.getMongo().host.indexOf(":");
diff --git a/jstests/core/dbcase.js b/jstests/core/dbcase.js
index 23b5bccd305..78d6e05f8ab 100644
--- a/jstests/core/dbcase.js
+++ b/jstests/core/dbcase.js
@@ -5,15 +5,15 @@
 //   multiple_tenants_incompatible,
 // ]
 
-a = db.getSiblingDB("dbcasetest_dbnamea");
-b = db.getSiblingDB("dbcasetest_dbnameA");
+let a = db.getSiblingDB("dbcasetest_dbnamea");
+let b = db.getSiblingDB("dbcasetest_dbnameA");
 
 a.dropDatabase();
 b.dropDatabase();
 
 assert.commandWorked(a.foo.save({x: 1}));
 
-res = b.foo.save({x: 1});
+let res = b.foo.save({x: 1});
 assert.writeError(res);
 
 assert.neq(-1, db.getMongo().getDBNames().indexOf(a.getName()));
@@ -23,8 +23,8 @@ printjson(db.getMongo().getDBs().databases);
 a.dropDatabase();
 b.dropDatabase();
 
-ai = db.getMongo().getDBNames().indexOf(a.getName());
-bi = db.getMongo().getDBNames().indexOf(b.getName());
+let ai = db.getMongo().getDBNames().indexOf(a.getName());
+let bi = db.getMongo().getDBNames().indexOf(b.getName());
 // One of these dbs may exist if there is a secondary active, but they must
 // not both exist.
 assert(ai == -1 || bi == -1);
diff --git a/jstests/core/dbhash.js b/jstests/core/dbhash.js
index c601c721f5b..33ee736e4b1 100644
--- a/jstests/core/dbhash.js
+++ b/jstests/core/dbhash.js
@@ -3,15 +3,15 @@
 //   not_allowed_with_security_token,
 // ]
 
-a = db.dbhasha;
-b = db.dbhashb;
+let a = db.dbhasha;
+let b = db.dbhashb;
 
 a.drop();
 b.drop();
 
 // debug SERVER-761
 db.getCollectionNames().forEach(function(x) {
-    v = db[x].validate();
+    let v = db[x].validate();
     if (!v.valid) {
         print(x);
         printjson(v);
@@ -45,8 +45,8 @@ assert.neq(gh(a), gh(b), "A2");
 b.insert({_id: 5});
 assert.eq(gh(a), gh(b), "A3");
 
-dba = db.getSiblingDB("dbhasha");
-dbb = db.getSiblingDB("dbhashb");
+let dba = db.getSiblingDB("dbhasha");
+let dbb = db.getSiblingDB("dbhashb");
 
 dba.dropDatabase();
 dbb.dropDatabase();
diff --git a/jstests/core/dbhash2.js b/jstests/core/dbhash2.js
index 93ec2abf99c..cf86a1a6d03 100644
--- a/jstests/core/dbhash2.js
+++ b/jstests/core/dbhash2.js
@@ -4,20 +4,20 @@
 //   assumes_superuser_permissions,
 // ]
 
-mydb = db.getSiblingDB("config");
+let mydb = db.getSiblingDB("config");
 
-t = mydb.foo;
+let t = mydb.foo;
 t.drop();
 
 assert.commandWorked(t.insert({x: 1}));
-res1 = mydb.runCommand("dbhash");
-res2 = mydb.runCommand("dbhash");
+let res1 = mydb.runCommand("dbhash");
+let res2 = mydb.runCommand("dbhash");
 assert.commandWorked(res1);
 assert.commandWorked(res2);
 assert.eq(res1.collections.foo, res2.collections.foo);
 
 assert.commandWorked(t.insert({x: 2}));
-res3 = mydb.runCommand("dbhash");
+let res3 = mydb.runCommand("dbhash");
 assert.commandWorked(res3);
 assert.neq(res1.collections.foo, res3.collections.foo);
 
diff --git a/jstests/core/ddl/bad_index_plugin.js b/jstests/core/ddl/bad_index_plugin.js
index c9cd549cc03..cb52ef0c1ab 100644
--- a/jstests/core/ddl/bad_index_plugin.js
+++ b/jstests/core/ddl/bad_index_plugin.js
@@ -1,5 +1,5 @@
 // SERVER-5826 ensure you can't build an index with a non-existent plugin
-t = db.bad_index_plugin;
+let t = db.bad_index_plugin;
 
 assert.commandWorked(t.createIndex({good: 1}));
 assert.eq(t.getIndexes().length, 2);  // good + _id
diff --git a/jstests/core/ddl/capped_convertToCapped1.js b/jstests/core/ddl/capped_convertToCapped1.js
index 137705c8661..4f51edc6c24 100644
--- a/jstests/core/ddl/capped_convertToCapped1.js
+++ b/jstests/core/ddl/capped_convertToCapped1.js
@@ -17,21 +17,21 @@
  * ]
  */
 
-source = db.capped_convertToCapped1;
-dest = db.capped_convertToCapped1_clone;
+let source = db.capped_convertToCapped1;
+let dest = db.capped_convertToCapped1_clone;
 
 source.drop();
 dest.drop();
 
-N = 1000;
+let N = 1000;
 
-for (i = 0; i < N; ++i) {
+for (let i = 0; i < N; ++i) {
     source.save({i: i});
 }
 assert.eq(N, source.count());
 
 // should all fit
-res = db.runCommand(
+let res = db.runCommand(
     {cloneCollectionAsCapped: source.getName(), toCollection: dest.getName(), size: 100000});
 assert.commandWorked(res);
 assert.eq(source.count(), dest.count());
diff --git a/jstests/core/ddl/create_indexes.js b/jstests/core/ddl/create_indexes.js
index 64598838466..3ab29ffb6a4 100644
--- a/jstests/core/ddl/create_indexes.js
+++ b/jstests/core/ddl/create_indexes.js
@@ -6,12 +6,13 @@
  */
 (function() {
 'use strict';
+load("jstests/libs/fixture_helpers.js");
 
 const kUnknownIDLFieldError = 40415;
-const isMongos = ("isdbgrid" == db.runCommand("hello").msg);
+const runningOnMongos = FixtureHelpers.isMongos(db);
 
 const extractResult = function(obj) {
-    if (!isMongos)
+    if (!runningOnMongos)
         return obj;
 
     // Sample mongos format:
diff --git a/jstests/core/ddl/drop3.js b/jstests/core/ddl/drop3.js
index 78d4872a6c0..7829b9cf310 100644
--- a/jstests/core/ddl/drop3.js
+++ b/jstests/core/ddl/drop3.js
@@ -4,8 +4,8 @@
 //   does_not_support_causal_consistency,
 // ]
 
-t = db.jstests_drop3;
-sub = t.sub;
+let t = db.jstests_drop3;
+let sub = t.sub;
 
 t.drop();
 sub.drop();
diff --git a/jstests/core/ddl/drop_index.js b/jstests/core/ddl/drop_index.js
index 3f3e815d47d..ed11b3a5e46 100644
--- a/jstests/core/ddl/drop_index.js
+++ b/jstests/core/ddl/drop_index.js
@@ -3,6 +3,7 @@
 // @tags: [assumes_no_implicit_index_creation]
 (function() {
 'use strict';
+load("jstests/libs/fixture_helpers.js");
 
 const t = db.drop_index;
 t.drop();
@@ -51,7 +52,7 @@ assertIndexes(['b_1', 'c_1', 'd_1', 'e_1'], 'dropping {a: 1} by name');
 assert.commandWorked(t.dropIndex({b: 1}));
 assertIndexes(['c_1', 'd_1', 'e_1'], 'dropping {b: 1} by key pattern');
 
-const isMongos = assert.commandWorked(db.runCommand("hello")).msg === "isdbgrid";
+const runningOnMongos = FixtureHelpers.isMongos(db);
 
 // Not allowed to drop _id index.
 for (const dropIndexArg of ['_id_', {_id: 1}]) {
@@ -59,7 +60,7 @@ for (const dropIndexArg of ['_id_', {_id: 1}]) {
     jsTestLog(`Reply to dropIndexes with arg ${tojson(dropIndexArg)}: ${tojson(dropIdIndexReply)}`);
     assert.commandFailedWithCode(dropIdIndexReply, ErrorCodes.InvalidOptions);
     assert(dropIdIndexReply.hasOwnProperty('errmsg'));
-    if (isMongos) {
+    if (runningOnMongos) {
         assert(dropIdIndexReply.hasOwnProperty('raw'));
     }
 }
diff --git a/jstests/core/ddl/rename_collection_capped.js b/jstests/core/ddl/rename_collection_capped.js
index 670e5ce611b..e0eb2efa9c3 100644
--- a/jstests/core/ddl/rename_collection_capped.js
+++ b/jstests/core/ddl/rename_collection_capped.js
@@ -13,9 +13,9 @@
  * ]
  */
 
-a = db.jstests_rename_a;
-b = db.jstests_rename_b;
-c = db.jstests_rename_c;
+let a = db.jstests_rename_a;
+let b = db.jstests_rename_b;
+let c = db.jstests_rename_c;
 
 a.drop();
 b.drop();
@@ -26,14 +26,14 @@ c.drop();
 // note we use floats to make sure numbers are represented as doubles for SpiderMonkey, since test
 // relies on record size
 db.createCollection("jstests_rename_a", {capped: true, size: 10000});
-for (i = 0.1; i < 10; ++i) {
+for (let i = 0.1; i < 10; ++i) {
     a.save({i: i});
 }
 assert.commandWorked(
     db.adminCommand({renameCollection: "test.jstests_rename_a", to: "test.jstests_rename_b"}));
 assert.eq(1, b.countDocuments({i: 9.1}));
 printjson(b.stats());
-for (i = 10.1; i < 1000; ++i) {
+for (var i = 10.1; i < 1000; ++i) {
     b.save({i: i});
 }
 printjson(b.stats());
diff --git a/jstests/core/ddl/rename_collection_staytemp.js b/jstests/core/ddl/rename_collection_staytemp.js
index 5db125f1a23..5107b399627 100644
--- a/jstests/core/ddl/rename_collection_staytemp.js
+++ b/jstests/core/ddl/rename_collection_staytemp.js
@@ -12,8 +12,8 @@
  * ]
  */
 
-orig = 'rename_stayTemp_orig';
-dest = 'rename_stayTemp_dest';
+let orig = 'rename_stayTemp_orig';
+let dest = 'rename_stayTemp_dest';
 
 db[orig].drop();
 db[dest].drop();
diff --git a/jstests/core/delx.js b/jstests/core/delx.js
index 331f6a18b67..b78e3051f8f 100644
--- a/jstests/core/delx.js
+++ b/jstests/core/delx.js
@@ -1,11 +1,11 @@
 // @tags: [assumes_against_mongod_not_mongos, requires_getmore, requires_non_retryable_writes]
 
-a = db.getSiblingDB("delxa");
-b = db.getSiblingDB("delxb");
+let a = db.getSiblingDB("delxa");
+let b = db.getSiblingDB("delxb");
 
 function setup(mydb) {
     mydb.dropDatabase();
-    for (i = 0; i < 100; i++) {
+    for (let i = 0; i < 100; i++) {
         mydb.foo.insert({_id: i});
     }
 }
@@ -16,8 +16,8 @@ setup(b);
 assert.eq(100, a.foo.find().itcount(), "A1");
 assert.eq(100, b.foo.find().itcount(), "A2");
 
-x = a.foo.find().sort({_id: 1}).batchSize(60);
-y = b.foo.find().sort({_id: 1}).batchSize(60);
+let x = a.foo.find().sort({_id: 1}).batchSize(60);
+let y = b.foo.find().sort({_id: 1}).batchSize(60);
 
 x.next();
 y.next();
@@ -27,7 +27,7 @@ a.foo.remove({_id: {$gt: 50}});
 assert.eq(51, a.foo.find().itcount(), "B1");
 assert.eq(100, b.foo.find().itcount(), "B2");
 
-xCount = x.itcount();
+let xCount = x.itcount();
 assert(xCount == 59 || xCount == 99, "C1 : " + xCount);  // snapshot or not is ok
 assert.eq(
     99,
diff --git a/jstests/core/error5.js b/jstests/core/error5.js
index edcfa059d25..fe4efef15e3 100644
--- a/jstests/core/error5.js
+++ b/jstests/core/error5.js
@@ -1,6 +1,6 @@
 // @tags: [requires_fastcount]
 
-t = db.error5;
+let t = db.error5;
 t.drop();
 
 assert.throws(function() {
diff --git a/jstests/core/hint1.js b/jstests/core/hint1.js
index d584144e641..09d328350c3 100644
--- a/jstests/core/hint1.js
+++ b/jstests/core/hint1.js
@@ -1,4 +1,4 @@
-p = db.jstests_hint1;
+let p = db.jstests_hint1;
 p.drop();
 
 p.save({ts: new Date(1), cls: "entry", verticals: "alleyinsider", live: true});
diff --git a/jstests/core/id1.js b/jstests/core/id1.js
index 79e26e33e90..a3fbaea3bfc 100644
--- a/jstests/core/id1.js
+++ b/jstests/core/id1.js
@@ -1,6 +1,6 @@
 // @tags: [requires_fastcount]
 
-t = db.id1;
+let t = db.id1;
 t.drop();
 
 t.save({_id: {a: 1, b: 2}, x: "a"});
diff --git a/jstests/core/index/covered/coveredIndex3.js b/jstests/core/index/covered/coveredIndex3.js
index 8b15b40e862..dd44f2544ea 100644
--- a/jstests/core/index/covered/coveredIndex3.js
+++ b/jstests/core/index/covered/coveredIndex3.js
@@ -6,8 +6,8 @@
 
 if (0) {  // SERVER-4975
 
-    t = db.jstests_coveredIndex3;
-    t2 = db.jstests_coveredIndex3_other;
+    let t = db.jstests_coveredIndex3;
+    let t2 = db.jstests_coveredIndex3_other;
     t.drop();
     t2.drop();
 
@@ -15,30 +15,30 @@ if (0) {  // SERVER-4975
         // Insert an array, which will make the { a:1 } index multikey and should disable covered
         // index
         // matching.
-        p1 = startParallelShell(
+        let p1 = startParallelShell(
             'for( i = 0; i < 60; ++i ) { \
                                db.jstests_coveredIndex3.save( { a:[ 2000, 2001 ] } ); \
                                sleep( 300 ); \
                            }');
 
         // Frequent writes cause the find operation to yield.
-        p2 = startParallelShell(
+        let p2 = startParallelShell(
             'for( i = 0; i < 1800; ++i ) { \
                             db.jstests_coveredIndex3_other.save( {} ); \
                             sleep( 10 ); \
                             }');
 
-        for (i = 0; i < 30; ++i) {
+        for (let i = 0; i < 30; ++i) {
             t.drop();
             t.createIndex({a: 1});
 
-            for (j = 0; j < 1000; ++j) {
+            for (let j = 0; j < 1000; ++j) {
                 t.save({a: j});
             }
 
-            c = t.find({}, {_id: 0, a: 1}).hint({a: 1}).batchSize(batchSize);
+            let c = t.find({}, {_id: 0, a: 1}).hint({a: 1}).batchSize(batchSize);
             while (c.hasNext()) {
-                o = c.next();
+                let o = c.next();
                 // If o contains a high numeric 'a' value, it must come from an array saved in p1.
                 assert(!(o.a > 1500), 'improper object returned ' + tojson(o));
             }
diff --git a/jstests/core/index/covered/coveredIndex4.js b/jstests/core/index/covered/coveredIndex4.js
index 7433ed7b9d6..b415328474e 100644
--- a/jstests/core/index/covered/coveredIndex4.js
+++ b/jstests/core/index/covered/coveredIndex4.js
@@ -5,14 +5,14 @@
 // Test covered index projection with $or clause, specifically in getMore
 // SERVER-4980
 
-t = db.jstests_coveredIndex4;
+let t = db.jstests_coveredIndex4;
 t.drop();
 
 t.createIndex({a: 1});
 t.createIndex({b: 1});
 
-orClause = [];
-for (i = 0; i < 200; ++i) {
+let orClause = [];
+for (let i = 0; i < 200; ++i) {
     if (i % 2 == 0) {
         t.save({a: i});
         orClause.push({a: i});
@@ -22,11 +22,11 @@ for (i = 0; i < 200; ++i) {
     }
 }
 
-c = t.find({$or: orClause}, {_id: 0, a: 1});
+let c = t.find({$or: orClause}, {_id: 0, a: 1});
 
 // No odd values of a were saved, so we should not see any in the results.
 while (c.hasNext()) {
-    o = c.next();
+    let o = c.next();
     if (o.a) {
         assert.eq(0, o.a % 2, 'unexpected result: ' + tojson(o));
     }
@@ -36,7 +36,7 @@ c = t.find({$or: orClause}, {_id: 0, b: 1});
 
 // No even values of b were saved, so we should not see any in the results.
 while (c.hasNext()) {
-    o = c.next();
+    let o = c.next();
     if (o.b) {
         assert.eq(1, o.b % 2, 'unexpected result: ' + tojson(o));
     }
diff --git a/jstests/core/index/covered/covered_index_compound_1.js b/jstests/core/index/covered/covered_index_compound_1.js
index 0efff371059..2227803a890 100644
--- a/jstests/core/index/covered/covered_index_compound_1.js
+++ b/jstests/core/index/covered/covered_index_compound_1.js
@@ -12,7 +12,7 @@ load("jstests/libs/analyze_plan.js");
 
 var coll = db.getCollection("covered_compound_1");
 coll.drop();
-for (i = 0; i < 100; i++) {
+for (let i = 0; i < 100; i++) {
     coll.insert({a: i, b: "strvar_" + (i % 13), c: NumberInt(i % 10)});
 }
 coll.createIndex({a: 1, b: -1, c: 1});
diff --git a/jstests/core/index/covered/covered_index_simple_1.js b/jstests/core/index/covered/covered_index_simple_1.js
index 16a6e3cdc6a..6b6db4ffe83 100644
--- a/jstests/core/index/covered/covered_index_simple_1.js
+++ b/jstests/core/index/covered/covered_index_simple_1.js
@@ -12,13 +12,13 @@ load("jstests/libs/analyze_plan.js");
 
 var coll = db.getCollection("covered_simple_1");
 coll.drop();
-for (i = 0; i < 10; i++) {
+for (let i = 0; i < 10; i++) {
     coll.insert({foo: i});
 }
-for (i = 0; i < 10; i++) {
+for (let i = 0; i < 10; i++) {
     coll.insert({foo: i});
 }
-for (i = 0; i < 5; i++) {
+for (let i = 0; i < 5; i++) {
     coll.insert({bar: i});
 }
 coll.insert({foo: "string"});
diff --git a/jstests/core/index/covered/covered_index_simple_2.js b/jstests/core/index/covered/covered_index_simple_2.js
index cf04f940ad0..6022bae3a5f 100644
--- a/jstests/core/index/covered/covered_index_simple_2.js
+++ b/jstests/core/index/covered/covered_index_simple_2.js
@@ -12,7 +12,7 @@ load("jstests/libs/analyze_plan.js");
 
 var coll = db.getCollection("covered_simple_2");
 coll.drop();
-for (i = 0; i < 10; i++) {
+for (let i = 0; i < 10; i++) {
     coll.insert({foo: i});
 }
 coll.insert({foo: "string"});
diff --git a/jstests/core/index/covered/covered_index_simple_3.js b/jstests/core/index/covered/covered_index_simple_3.js
index 4beff2b3c5a..5c8402803c1 100644
--- a/jstests/core/index/covered/covered_index_simple_3.js
+++ b/jstests/core/index/covered/covered_index_simple_3.js
@@ -12,10 +12,10 @@ load("jstests/libs/analyze_plan.js");
 
 var coll = db.getCollection("covered_simple_3");
 coll.drop();
-for (i = 0; i < 10; i++) {
+for (let i = 0; i < 10; i++) {
     coll.insert({foo: i});
 }
-for (i = 0; i < 5; i++) {
+for (let i = 0; i < 5; i++) {
     coll.insert({bar: i});
 }
 coll.insert({foo: "string"});
diff --git a/jstests/core/index/covered/covered_index_simple_id.js b/jstests/core/index/covered/covered_index_simple_id.js
index 59efcd7f13a..6fc7279f56d 100644
--- a/jstests/core/index/covered/covered_index_simple_id.js
+++ b/jstests/core/index/covered/covered_index_simple_id.js
@@ -9,7 +9,7 @@ load("jstests/libs/analyze_plan.js");
 
 var coll = db.getCollection("covered_simple_id");
 coll.drop();
-for (i = 0; i < 10; i++) {
+for (let i = 0; i < 10; i++) {
     coll.insert({_id: i});
 }
 coll.insert({_id: "string"});
diff --git a/jstests/core/index/covered/covered_index_sort_1.js b/jstests/core/index/covered/covered_index_sort_1.js
index 499bff128e7..d1f1803f1e1 100644
--- a/jstests/core/index/covered/covered_index_sort_1.js
+++ b/jstests/core/index/covered/covered_index_sort_1.js
@@ -12,13 +12,13 @@ load("jstests/libs/analyze_plan.js");
 
 var coll = db.getCollection("covered_sort_1");
 coll.drop();
-for (i = 0; i < 10; i++) {
+for (let i = 0; i < 10; i++) {
     coll.insert({foo: i});
 }
-for (i = 0; i < 10; i++) {
+for (let i = 0; i < 10; i++) {
     coll.insert({foo: i});
 }
-for (i = 0; i < 5; i++) {
+for (let i = 0; i < 5; i++) {
     coll.insert({bar: i});
 }
 coll.insert({foo: "1"});
diff --git a/jstests/core/index/covered/covered_index_sort_2.js b/jstests/core/index/covered/covered_index_sort_2.js
index 736a48bb452..4818b325a02 100644
--- a/jstests/core/index/covered/covered_index_sort_2.js
+++ b/jstests/core/index/covered/covered_index_sort_2.js
@@ -9,7 +9,7 @@ load("jstests/libs/analyze_plan.js");
 
 var coll = db.getCollection("covered_sort_2");
 coll.drop();
-for (i = 0; i < 10; i++) {
+for (let i = 0; i < 10; i++) {
     coll.insert({_id: i});
 }
 coll.insert({_id: "1"});
diff --git a/jstests/core/index/covered/covered_index_sort_3.js b/jstests/core/index/covered/covered_index_sort_3.js
index 9e57a79a2a2..dc6b2dc25e6 100644
--- a/jstests/core/index/covered/covered_index_sort_3.js
+++ b/jstests/core/index/covered/covered_index_sort_3.js
@@ -12,7 +12,7 @@ load("jstests/libs/analyze_plan.js");
 
 var coll = db.getCollection("covered_sort_3");
 coll.drop();
-for (i = 0; i < 100; i++) {
+for (let i = 0; i < 100; i++) {
     coll.insert({a: i, b: "strvar_" + (i % 13), c: NumberInt(i % 10)});
 }
 
diff --git a/jstests/core/index/fts/fts2.js b/jstests/core/index/fts/fts2.js
index 79be057fed8..418a8ca3215 100644
--- a/jstests/core/index/fts/fts2.js
+++ b/jstests/core/index/fts/fts2.js
@@ -1,6 +1,6 @@
 load("jstests/libs/fts.js");
 
-t = db.text2;
+let t = db.text2;
 t.drop();
 
 t.save({_id: 1, x: "az b x", y: "c d m", z: 1});
diff --git a/jstests/core/index/fts/fts3.js b/jstests/core/index/fts/fts3.js
index 9b89cda029c..b28227e57bb 100644
--- a/jstests/core/index/fts/fts3.js
+++ b/jstests/core/index/fts/fts3.js
@@ -1,6 +1,6 @@
 load("jstests/libs/fts.js");
 
-t = db.text3;
+let t = db.text3;
 t.drop();
 
 t.save({_id: 1, x: "az b x", y: "c d m", z: 1});
diff --git a/jstests/core/index/fts/fts4.js b/jstests/core/index/fts/fts4.js
index bb19fba2221..3e92b6f0574 100644
--- a/jstests/core/index/fts/fts4.js
+++ b/jstests/core/index/fts/fts4.js
@@ -1,6 +1,6 @@
 load("jstests/libs/fts.js");
 
-t = db.text4;
+let t = db.text4;
 t.drop();
 
 t.save({_id: 1, x: ["az", "b", "x"], y: ["c", "d", "m"], z: 1});
diff --git a/jstests/core/index/fts/fts5.js b/jstests/core/index/fts/fts5.js
index 28d9b48d957..13bde38545b 100644
--- a/jstests/core/index/fts/fts5.js
+++ b/jstests/core/index/fts/fts5.js
@@ -1,6 +1,6 @@
 load("jstests/libs/fts.js");
 
-t = db.text5;
+let t = db.text5;
 t.drop();
 
 t.save({_id: 1, x: [{a: "az"}, {a: "b"}, {a: "x"}], y: ["c", "d", "m"], z: 1});
diff --git a/jstests/core/index/fts/fts_blog.js b/jstests/core/index/fts/fts_blog.js
index 5208c166258..5b7b7559512 100644
--- a/jstests/core/index/fts/fts_blog.js
+++ b/jstests/core/index/fts/fts_blog.js
@@ -1,4 +1,4 @@
-t = db.text_blog;
+let t = db.text_blog;
 t.drop();
 
 t.save({_id: 1, title: "my blog post", text: "this is a new blog i am writing. yay"});
@@ -9,7 +9,7 @@ t.save({_id: 3, title: "knives are Fun", text: "this is a new blog i am writing.
 // specify weights if you want a field to be more meaningull
 t.createIndex({"title": "text", text: "text"}, {weights: {title: 10}});
 
-res = t.find({"$text": {"$search": "blog"}}, {score: {"$meta": "textScore"}}).sort({
+let res = t.find({"$text": {"$search": "blog"}}, {score: {"$meta": "textScore"}}).sort({
     score: {"$meta": "textScore"}
 });
 assert.eq(3, res.length());
diff --git a/jstests/core/index/fts/fts_blogwild.js b/jstests/core/index/fts/fts_blogwild.js
index f449b6b827e..ffb28533e11 100644
--- a/jstests/core/index/fts/fts_blogwild.js
+++ b/jstests/core/index/fts/fts_blogwild.js
@@ -4,7 +4,7 @@
 //   assumes_no_implicit_index_creation,
 // ]
 
-t = db.text_blogwild;
+let t = db.text_blogwild;
 t.drop();
 
 t.save({_id: 1, title: "my blog post", text: "this is a new blog i am writing. yay eliot"});
@@ -21,7 +21,7 @@ t.createIndex({dummy: "text"}, {weights: "$**"});
 // ensure listIndexes can handle a string-valued "weights"
 assert.eq(2, t.getIndexes().length);
 
-res = t.find({"$text": {"$search": "blog"}});
+let res = t.find({"$text": {"$search": "blog"}});
 assert.eq(3, res.length(), "A1");
 
 res = t.find({"$text": {"$search": "write"}});
diff --git a/jstests/core/index/fts/fts_partition1.js b/jstests/core/index/fts/fts_partition1.js
index 4a26a3ad629..3791c461f7d 100644
--- a/jstests/core/index/fts/fts_partition1.js
+++ b/jstests/core/index/fts/fts_partition1.js
@@ -1,6 +1,6 @@
 load("jstests/libs/fts.js");
 
-t = db.text_parition1;
+let t = db.text_parition1;
 t.drop();
 
 t.insert({_id: 1, x: 1, y: "foo"});
@@ -19,7 +19,7 @@ assert.throws(function() {
 
 assert.eq([1], queryIDS(t, "foo", {x: 1}));
 
-res = t.find({"$text": {"$search": "foo"}, x: 1}, {score: {"$meta": "textScore"}});
+let res = t.find({"$text": {"$search": "foo"}, x: 1}, {score: {"$meta": "textScore"}});
 assert(res[0].score > 0, tojson(res.toArray()));
 
 // repeat "search" with "language" specified, SERVER-8999
diff --git a/jstests/core/index/fts/fts_partition_no_multikey.js b/jstests/core/index/fts/fts_partition_no_multikey.js
index b819c3abfbd..c8adead6100 100644
--- a/jstests/core/index/fts/fts_partition_no_multikey.js
+++ b/jstests/core/index/fts/fts_partition_no_multikey.js
@@ -1,4 +1,4 @@
-t = db.fts_partition_no_multikey;
+let t = db.fts_partition_no_multikey;
 t.drop();
 
 t.createIndex({x: 1, y: "text"});
diff --git a/jstests/core/index/fts/fts_phrase.js b/jstests/core/index/fts/fts_phrase.js
index 1a3d7470326..31356e8a4ea 100644
--- a/jstests/core/index/fts/fts_phrase.js
+++ b/jstests/core/index/fts/fts_phrase.js
@@ -1,4 +1,4 @@
-t = db.text_phrase;
+let t = db.text_phrase;
 t.drop();
 
 t.save({_id: 1, title: "my blog post", text: "i am writing a blog. yay"});
@@ -7,7 +7,7 @@ t.save({_id: 3, title: "knives are Fun", text: "this is a new blog i am writing.
 
 t.createIndex({"title": "text", text: "text"}, {weights: {title: 10}});
 
-res = t.find({"$text": {"$search": "blog write"}}, {score: {"$meta": "textScore"}}).sort({
+let res = t.find({"$text": {"$search": "blog write"}}, {score: {"$meta": "textScore"}}).sort({
     score: {"$meta": "textScore"}
 });
 assert.eq(3, res.length());
diff --git a/jstests/core/index/geo/geo1.js b/jstests/core/index/geo/geo1.js
index 8a80f59d692..126aae3505d 100644
--- a/jstests/core/index/geo/geo1.js
+++ b/jstests/core/index/geo/geo1.js
@@ -5,13 +5,10 @@
 //   requires_fastcount,
 // ]
 
-t = db.geo1;
+let t = db.geo1;
 t.drop();
 
-idx = {
-    loc: "2d",
-    zip: 1
-};
+let idx = {loc: "2d", zip: 1};
 
 t.insert({zip: "06525", loc: [41.352964, 73.01212]});
 t.insert({zip: "10024", loc: [40.786387, 73.97709]});
@@ -31,7 +28,7 @@ assert.eq(3, t.count(), "B3");
 
 // test normal access
 
-wb = t.findOne({zip: "06525"});
+let wb = t.findOne({zip: "06525"});
 assert(wb, "C1");
 
 assert.eq("06525", t.find({loc: wb.loc}).hint({"$natural": 1})[0].zip, "C2");
diff --git a/jstests/core/index/geo/geo10.js b/jstests/core/index/geo/geo10.js
index 45463711406..adbf0862cbe 100644
--- a/jstests/core/index/geo/geo10.js
+++ b/jstests/core/index/geo/geo10.js
@@ -6,7 +6,7 @@
 
 // Test for SERVER-2746
 
-coll = db.geo10;
+let coll = db.geo10;
 coll.drop();
 
 assert.commandWorked(db.geo10.createIndex({c: '2d', t: 1}, {min: 0, max: Math.pow(2, 40)}));
diff --git a/jstests/core/index/geo/geo2.js b/jstests/core/index/geo/geo2.js
index 34588acac9e..e4521b5b45e 100644
--- a/jstests/core/index/geo/geo2.js
+++ b/jstests/core/index/geo/geo2.js
@@ -3,11 +3,11 @@
 //   requires_fastcount,
 // ]
 
-t = db.geo2;
+let t = db.geo2;
 t.drop();
 
-n = 1;
-arr = [];
+let n = 1;
+let arr = [];
 for (var x = -100; x < 100; x += 2) {
     for (var y = -100; y < 100; y += 2) {
         arr.push({_id: n++, loc: [x, y]});
diff --git a/jstests/core/index/geo/geo3.js b/jstests/core/index/geo/geo3.js
index 7e54fd7dc5f..381ec12f399 100644
--- a/jstests/core/index/geo/geo3.js
+++ b/jstests/core/index/geo/geo3.js
@@ -4,11 +4,11 @@
 // ]
 
 (function() {
-t = db.geo3;
+let t = db.geo3;
 t.drop();
 
-n = 1;
-arr = [];
+let n = 1;
+let arr = [];
 for (var x = -100; x < 100; x += 2) {
     for (var y = -100; y < 100; y += 2) {
         arr.push({_id: n++, loc: [x, y], a: Math.abs(x) % 5, b: Math.abs(y) % 5});
@@ -67,9 +67,7 @@ assert.commandWorked(t.createIndex({loc: "2d", b: 1}));
 
 testFiltering("loc and b");
 
-q = {
-    loc: {$near: [50, 50]}
-};
+let q = {loc: {$near: [50, 50]}};
 assert.eq(100, t.find(q).limit(100).itcount(), "D1");
 assert.eq(100, t.find(q).limit(100).size(), "D2");
 
diff --git a/jstests/core/index/geo/geo6.js b/jstests/core/index/geo/geo6.js
index 8d32c066c88..98022ad7940 100644
--- a/jstests/core/index/geo/geo6.js
+++ b/jstests/core/index/geo/geo6.js
@@ -1,4 +1,4 @@
-t = db.geo6;
+let t = db.geo6;
 t.drop();
 
 t.createIndex({loc: "2d"});
diff --git a/jstests/core/index/geo/geo9.js b/jstests/core/index/geo/geo9.js
index 6b1bfb60631..701c6bd6680 100644
--- a/jstests/core/index/geo/geo9.js
+++ b/jstests/core/index/geo/geo9.js
@@ -1,4 +1,4 @@
-t = db.geo9;
+let t = db.geo9;
 t.drop();
 
 t.save({_id: 1, a: [10, 10], b: [50, 50]});
@@ -15,7 +15,7 @@ t.createIndex({b: "2d"});
 function check(field) {
     var q = {};
     q[field] = {$near: [11, 11]};
-    arr = t.find(q).limit(3).map(function(z) {
+    let arr = t.find(q).limit(3).map(function(z) {
         return Geo.distance([11, 11], z[field]);
     });
     assert.eq(2 * Math.sqrt(2), Array.sum(arr), "test " + field);
diff --git a/jstests/core/index/geo/geo_allowedcomparisons.js b/jstests/core/index/geo/geo_allowedcomparisons.js
index 2f689f4be68..80ea1e25fee 100644
--- a/jstests/core/index/geo/geo_allowedcomparisons.js
+++ b/jstests/core/index/geo/geo_allowedcomparisons.js
@@ -1,33 +1,27 @@
 // A test for what geometries can interact with what other geometries.
-t = db.geo_allowedcomparisons;
+let t = db.geo_allowedcomparisons;
 
 // Any GeoJSON object can intersect with any geojson object.
-geojsonPoint = {
-    "type": "Point",
-    "coordinates": [0, 0]
-};
-oldPoint = [0, 0];
+let geojsonPoint = {"type": "Point", "coordinates": [0, 0]};
+let oldPoint = [0, 0];
 
 // GeoJSON polygons can contain any geojson object and OLD points.
-geojsonPoly = {
+let geojsonPoly = {
     "type": "Polygon",
     "coordinates": [[[-5, -5], [-5, 5], [5, 5], [5, -5], [-5, -5]]]
 };
 
 // This can be contained by GJ polygons, intersected by anything GJ and old points.
-geojsonLine = {
-    "type": "LineString",
-    "coordinates": [[0, 0], [1, 1]]
-};
+let geojsonLine = {"type": "LineString", "coordinates": [[0, 0], [1, 1]]};
 
 // $centerSphere can contain old or new points.
-oldCenterSphere = [[0, 0], Math.PI / 180];
+let oldCenterSphere = [[0, 0], Math.PI / 180];
 // $box can contain old points.
-oldBox = [[-5, -5], [5, 5]];
+let oldBox = [[-5, -5], [5, 5]];
 // $polygon can contain old points.
-oldPolygon = [[-5, -5], [-5, 5], [5, 5], [5, -5], [-5, -5]];
+let oldPolygon = [[-5, -5], [-5, 5], [5, 5], [5, -5], [-5, -5]];
 // $center can contain old points.
-oldCenter = [[0, 0], 1];
+let oldCenter = [[0, 0], 1];
 
 t.drop();
 t.createIndex({geo: "2d"});
@@ -47,10 +41,7 @@ assert.writeError(t.insert({geo: oldCenter}));
 // Verify that even if we can't index them, we can use them in a matcher.
 t.insert({gj: geojsonLine});
 t.insert({gj: geojsonPoly});
-geojsonPoint2 = {
-    "type": "Point",
-    "coordinates": [0, 0.001]
-};
+let geojsonPoint2 = {"type": "Point", "coordinates": [0, 0.001]};
 t.insert({gjp: geojsonPoint2});
 
 // We convert between old and new style points.
diff --git a/jstests/core/index/geo/geo_array0.js b/jstests/core/index/geo/geo_array0.js
index 0c9dc096afb..29798952d60 100644
--- a/jstests/core/index/geo/geo_array0.js
+++ b/jstests/core/index/geo/geo_array0.js
@@ -5,7 +5,7 @@
 // ]
 
 // Make sure the very basics of geo arrays are sane by creating a few multi location docs
-t = db.geoarray;
+let t = db.geoarray;
 
 function test(index) {
     t.drop();
diff --git a/jstests/core/index/geo/geo_array2.js b/jstests/core/index/geo/geo_array2.js
index 7da56a576eb..7e09608c07e 100644
--- a/jstests/core/index/geo/geo_array2.js
+++ b/jstests/core/index/geo/geo_array2.js
@@ -1,6 +1,6 @@
 // Check the semantics of near calls with multiple locations
 
-t = db.geoarray2;
+let t = db.geoarray2;
 t.drop();
 
 var numObjs = 10;
@@ -12,7 +12,7 @@ Random.setRandomSeed();
 
 for (var i = -1; i < 2; i++) {
     for (var j = -1; j < 2; j++) {
-        locObj = [];
+        let locObj = [];
 
         if (i != 0 || j != 0)
             locObj.push({x: i * 50 + Random.rand(), y: j * 50 + Random.rand()});
@@ -28,7 +28,7 @@ assert.commandWorked(t.createIndex({loc: "2d", type: 1}));
 
 print("Starting testing phase... ");
 
-for (var t = 0; t < 2; t++) {
+for (let t = 0; t < 2; t++) {
     var type = t == 0 ? "A" : "B";
 
     for (var i = -1; i < 2; i++) {
diff --git a/jstests/core/index/geo/geo_big_polygon2.js b/jstests/core/index/geo/geo_big_polygon2.js
index 389bc9ef7bc..a4dc09a132e 100644
--- a/jstests/core/index/geo/geo_big_polygon2.js
+++ b/jstests/core/index/geo/geo_big_polygon2.js
@@ -461,9 +461,9 @@ function nGonGenerator(N, D, clockwise, LON, LAT) {
             lat = (-D / 2);
         }
         lon = Math.sqrt((D / 2) * (D / 2) - (lat * lat));
-        newlat = lat + LAT;
-        newlon = lon + LON;
-        conjugateLon = LON - lon;
+        let newlat = lat + LAT;
+        let newlon = lon + LON;
+        let conjugateLon = LON - lon;
         pts[i] = [newlon, newlat];
         pts[N - i] = [conjugateLon, newlat];
     }
diff --git a/jstests/core/index/geo/geo_borders.js b/jstests/core/index/geo/geo_borders.js
index 897697a88cb..09b89c0d753 100644
--- a/jstests/core/index/geo/geo_borders.js
+++ b/jstests/core/index/geo/geo_borders.js
@@ -4,16 +4,16 @@
  * ]
  */
 
-t = db.borders;
+let t = db.borders;
 t.drop();
 
-epsilon = 0.0001;
+let epsilon = 0.0001;
 
 // For these tests, *required* that step ends exactly on max
-min = -1;
-max = 1;
-step = 1;
-numItems = 0;
+let min = -1;
+let max = 1;
+let step = 1;
+let numItems = 0;
 
 for (var x = min; x <= max; x += step) {
     for (var y = min; y <= max; y += step) {
@@ -22,8 +22,8 @@ for (var x = min; x <= max; x += step) {
     }
 }
 
-overallMin = -1;
-overallMax = 1;
+let overallMin = -1;
+let overallMax = 1;
 
 // Create a point index slightly smaller than the points we have
 var res =
@@ -113,14 +113,14 @@ assert.eq(numItems, t.find({
 // Circle tests
 // **************
 
-center = (overallMax + overallMin) / 2;
+let center = (overallMax + overallMin) / 2;
 center = [center, center];
-radius = overallMax;
+let radius = overallMax;
 
-offCenter = [center[0] + radius, center[1] + radius];
-onBounds = [offCenter[0] + epsilon, offCenter[1] + epsilon];
-offBounds = [onBounds[0] + epsilon, onBounds[1] + epsilon];
-onBoundsNeg = [-onBounds[0], -onBounds[1]];
+let offCenter = [center[0] + radius, center[1] + radius];
+let onBounds = [offCenter[0] + epsilon, offCenter[1] + epsilon];
+let offBounds = [onBounds[0] + epsilon, onBounds[1] + epsilon];
+let onBoundsNeg = [-onBounds[0], -onBounds[1]];
 
 // Make sure we can get all points when radius is exactly at full bounds
 assert.lt(0, t.find({loc: {$within: {$center: [center, radius + epsilon]}}}).count());
@@ -133,7 +133,7 @@ assert.lt(0, t.find({loc: {$within: {$center: [offCenter, radius + 2 * epsilon]}
 
 // Make sure we get correct corner point when center is in bounds
 // (x bounds wrap, so could get other corner)
-cornerPt = t.findOne({loc: {$within: {$center: [offCenter, step / 2]}}});
+let cornerPt = t.findOne({loc: {$within: {$center: [offCenter, step / 2]}}});
 assert.eq(cornerPt.loc.y, overallMax);
 
 // Make sure we get correct corner point when center is on bounds
diff --git a/jstests/core/index/geo/geo_box1.js b/jstests/core/index/geo/geo_box1.js
index d0c4ff50bdf..40a754d64b3 100644
--- a/jstests/core/index/geo/geo_box1.js
+++ b/jstests/core/index/geo/geo_box1.js
@@ -2,32 +2,32 @@
 //   requires_getmore,
 // ]
 
-t = db.geo_box1;
+let t = db.geo_box1;
 t.drop();
 
-num = 0;
-for (x = 0; x <= 20; x++) {
-    for (y = 0; y <= 20; y++) {
-        o = {_id: num++, loc: [x, y]};
+let num = 0;
+for (let x = 0; x <= 20; x++) {
+    for (let y = 0; y <= 20; y++) {
+        let o = {_id: num++, loc: [x, y]};
         t.save(o);
     }
 }
 
 t.createIndex({loc: "2d"});
 
-searches = [
+let searches = [
     [[1, 2], [4, 5]],
     [[1, 1], [2, 2]],
     [[0, 2], [4, 5]],
     [[1, 1], [2, 8]],
 ];
 
-for (i = 0; i < searches.length; i++) {
-    b = searches[i];
+for (let i = 0; i < searches.length; i++) {
+    let b = searches[i];
     // printjson( b );
 
-    q = {loc: {$within: {$box: b}}};
-    numWanetd = (1 + b[1][0] - b[0][0]) * (1 + b[1][1] - b[0][1]);
+    let q = {loc: {$within: {$box: b}}};
+    let numWanetd = (1 + b[1][0] - b[0][0]) * (1 + b[1][1] - b[0][1]);
     assert.eq(numWanetd, t.find(q).itcount(), "itcount: " + tojson(q));
     printjson(t.find(q).explain());
 }
diff --git a/jstests/core/index/geo/geo_box1_noindex.js b/jstests/core/index/geo/geo_box1_noindex.js
index 879f17e3002..3da72a96b44 100644
--- a/jstests/core/index/geo/geo_box1_noindex.js
+++ b/jstests/core/index/geo/geo_box1_noindex.js
@@ -3,28 +3,28 @@
 // ]
 
 // SERVER-7343: allow $within without a geo index.
-t = db.geo_box1_noindex;
+let t = db.geo_box1_noindex;
 t.drop();
 
-num = 0;
-for (x = 0; x <= 20; x++) {
-    for (y = 0; y <= 20; y++) {
-        o = {_id: num++, loc: [x, y]};
+let num = 0;
+for (let x = 0; x <= 20; x++) {
+    for (let y = 0; y <= 20; y++) {
+        let o = {_id: num++, loc: [x, y]};
         t.save(o);
     }
 }
 
-searches = [
+let searches = [
     [[1, 2], [4, 5]],
     [[1, 1], [2, 2]],
     [[0, 2], [4, 5]],
     [[1, 1], [2, 8]],
 ];
 
-for (i = 0; i < searches.length; i++) {
-    b = searches[i];
-    q = {loc: {$within: {$box: b}}};
-    numWanted = (1 + b[1][0] - b[0][0]) * (1 + b[1][1] - b[0][1]);
+for (let i = 0; i < searches.length; i++) {
+    let b = searches[i];
+    let q = {loc: {$within: {$box: b}}};
+    let numWanted = (1 + b[1][0] - b[0][0]) * (1 + b[1][1] - b[0][1]);
     assert.eq(numWanted, t.find(q).itcount(), "itcount: " + tojson(q));
     printjson(t.find(q).explain());
 }
diff --git a/jstests/core/index/geo/geo_box2.js b/jstests/core/index/geo/geo_box2.js
index 7120cfd3e4a..60c76603b5b 100644
--- a/jstests/core/index/geo/geo_box2.js
+++ b/jstests/core/index/geo/geo_box2.js
@@ -1,9 +1,9 @@
-t = db.geo_box2;
+let t = db.geo_box2;
 
 t.drop();
 
-for (i = 1; i < 10; i++) {
-    for (j = 1; j < 10; j++) {
+for (let i = 1; i < 10; i++) {
+    for (let j = 1; j < 10; j++) {
         t.insert({loc: [i, j]});
     }
 }
diff --git a/jstests/core/index/geo/geo_box3.js b/jstests/core/index/geo/geo_box3.js
index 4a91ffb0d1d..3ca3d4b82e3 100644
--- a/jstests/core/index/geo/geo_box3.js
+++ b/jstests/core/index/geo/geo_box3.js
@@ -4,7 +4,7 @@
 // bounding box.
 
 // This is the bug reported in SERVER-994.
-t = db.geo_box3;
+let t = db.geo_box3;
 t.drop();
 t.insert({point: {x: -15000000, y: 10000000}});
 t.createIndex({point: "2d"}, {min: -21000000, max: 21000000});
diff --git a/jstests/core/index/geo/geo_center_sphere1.js b/jstests/core/index/geo/geo_center_sphere1.js
index 2b37c7c3f96..c3cdb5aa7d0 100644
--- a/jstests/core/index/geo/geo_center_sphere1.js
+++ b/jstests/core/index/geo/geo_center_sphere1.js
@@ -3,13 +3,14 @@
 //   requires_fastcount,
 // ]
 
-t = db.geo_center_sphere1;
+let t = db.geo_center_sphere1;
 
 function test(index) {
     t.drop();
-    skip = 8;  // lower for more rigor, higher for more speed (tested with .5, .678, 1, 2, 3, and 4)
+    let skip =
+        8;  // lower for more rigor, higher for more speed (tested with .5, .678, 1, 2, 3, and 4)
 
-    searches = [
+    let searches = [
         //  x , y    rad
         [[5, 0], 0.05],  // ~200 miles
         [[135, 0], 0.05],
@@ -23,18 +24,18 @@ function test(index) {
         [[-20, 60], 0.25],
         [[-20, -70], 0.25],
     ];
-    correct = searches.map(function(z) {
+    let correct = searches.map(function(z) {
         return [];
     });
 
-    num = 0;
+    let num = 0;
 
     var bulk = t.initializeUnorderedBulkOp();
-    for (x = -179; x <= 179; x += skip) {
-        for (y = -89; y <= 89; y += skip) {
-            o = {_id: num++, loc: [x, y]};
+    for (let x = -179; x <= 179; x += skip) {
+        for (let y = -89; y <= 89; y += skip) {
+            let o = {_id: num++, loc: [x, y]};
             bulk.insert(o);
-            for (i = 0; i < searches.length; i++) {
+            for (let i = 0; i < searches.length; i++) {
                 if (Geo.sphereDistance([x, y], searches[i][0]) <= searches[i][1])
                     correct[i].push(o);
             }
@@ -47,10 +48,10 @@ function test(index) {
         t.createIndex({loc: index});
     }
 
-    for (i = 0; i < searches.length; i++) {
+    for (let i = 0; i < searches.length; i++) {
         print('------------');
         print(tojson(searches[i]) + "\t" + correct[i].length);
-        q = {loc: {$within: {$centerSphere: searches[i]}}};
+        let q = {loc: {$within: {$centerSphere: searches[i]}}};
 
         // correct[i].forEach( printjson )
         // printjson( q );
@@ -69,8 +70,8 @@ function test(index) {
             return z._id;
         });
 
-        missing = [];
-        epsilon = 0.001;  // allow tenth of a percent error due to conversions
+        let missing = [];
+        let epsilon = 0.001;  // allow tenth of a percent error due to conversions
         for (var j = 0; j < x.length; j++) {
             if (!Array.contains(y, x[j])) {
                 missing.push(x[j]);
diff --git a/jstests/core/index/geo/geo_center_sphere2.js b/jstests/core/index/geo/geo_center_sphere2.js
index 1c59850d841..ecf3622217c 100644
--- a/jstests/core/index/geo/geo_center_sphere2.js
+++ b/jstests/core/index/geo/geo_center_sphere2.js
@@ -18,8 +18,8 @@ function computexscandist(y, maxDistDegrees) {
 }
 
 function pointIsOK(startPoint, radius) {
-    yscandist = rad2deg(radius) + 0.01;
-    xscandist = computexscandist(startPoint[1], yscandist);
+    let yscandist = rad2deg(radius) + 0.01;
+    let xscandist = computexscandist(startPoint[1], yscandist);
     return (startPoint[0] + xscandist < 180) && (startPoint[0] - xscandist > -180) &&
         (startPoint[1] + yscandist < 90) && (startPoint[1] - yscandist > -90);
 }
diff --git a/jstests/core/index/geo/geo_circle2.js b/jstests/core/index/geo/geo_circle2.js
index d7947f96502..1d228db988c 100644
--- a/jstests/core/index/geo/geo_circle2.js
+++ b/jstests/core/index/geo/geo_circle2.js
@@ -1,4 +1,4 @@
-t = db.geo_circle2;
+let t = db.geo_circle2;
 t.drop();
 
 t.createIndex({loc: "2d", categories: 1}, {"name": "placesIdx", "min": -100, "max": 100});
diff --git a/jstests/core/index/geo/geo_circle3.js b/jstests/core/index/geo/geo_circle3.js
index da7a9af6b34..9466f1e0c5f 100644
--- a/jstests/core/index/geo/geo_circle3.js
+++ b/jstests/core/index/geo/geo_circle3.js
@@ -1,7 +1,7 @@
 // SERVER-848 and SERVER-1191.
 db.places.drop();
 
-n = 0;
+let n = 0;
 db.places.save({"_id": n++, "loc": {"x": 4.9999, "y": 52}});
 db.places.save({"_id": n++, "loc": {"x": 5, "y": 52}});
 db.places.save({"_id": n++, "loc": {"x": 5.0001, "y": 52}});
@@ -12,8 +12,8 @@ db.places.save({"_id": n++, "loc": {"x": 5.0001, "y": 52.0001}});
 db.places.save({"_id": n++, "loc": {"x": 4.9999, "y": 51.9999}});
 db.places.save({"_id": n++, "loc": {"x": 5.0001, "y": 51.9999}});
 db.places.createIndex({loc: "2d"});
-radius = 0.0001;
-center = [5, 52];
+let radius = 0.0001;
+let center = [5, 52];
 // print(db.places.find({"loc" : {"$within" : {"$center" : [center, radius]}}}).count())
 // FIXME: we want an assert, e.g., that there be 5 answers in the find().
 db.places.find({"loc": {"$within": {"$center": [center, radius]}}}).forEach(printjson);
diff --git a/jstests/core/index/geo/geo_circle4.js b/jstests/core/index/geo/geo_circle4.js
index c2194142795..50cff15512f 100644
--- a/jstests/core/index/geo/geo_circle4.js
+++ b/jstests/core/index/geo/geo_circle4.js
@@ -2,8 +2,8 @@
 function test(index) {
     db.server848.drop();
 
-    radius = 0.0001;
-    center = [5, 52];
+    let radius = 0.0001;
+    let center = [5, 52];
 
     db.server848.save({"_id": 1, "loc": {"x": 4.9999, "y": 52}});
     db.server848.save({"_id": 2, "loc": {"x": 5, "y": 52}});
@@ -17,12 +17,12 @@ function test(index) {
     if (index) {
         db.server848.createIndex({loc: "2d"});
     }
-    r = db.server848.find({"loc": {"$within": {"$center": [center, radius]}}}, {_id: 1});
+    let r = db.server848.find({"loc": {"$within": {"$center": [center, radius]}}}, {_id: 1});
     assert.eq(5, r.count(), "A1");
     // FIXME: surely code like this belongs in utils.js.
-    a = r.toArray();
-    x = [];
-    for (k in a) {
+    let a = r.toArray();
+    let x = [];
+    for (let k in a) {
         x.push(a[k]["_id"]);
     }
     x.sort();
diff --git a/jstests/core/index/geo/geo_circle5.js b/jstests/core/index/geo/geo_circle5.js
index 27b973a8ede..4f43d8b3bec 100644
--- a/jstests/core/index/geo/geo_circle5.js
+++ b/jstests/core/index/geo/geo_circle5.js
@@ -12,9 +12,9 @@ db.server1238.createIndex({loc: "2d"}, {min: -21000000, max: 21000000});
 db.server1238.save({loc: [5000000, 900000], id: 3});
 db.server1238.save({loc: [5000000, 900000], id: 4});
 
-c1 = db.server1238.find({"loc": {"$within": {"$center": [[5000000, 900000], 1.0]}}}).count();
+let c1 = db.server1238.find({"loc": {"$within": {"$center": [[5000000, 900000], 1.0]}}}).count();
 
-c2 = db.server1238.find({"loc": {"$within": {"$center": [[5000001, 900000], 5.0]}}}).count();
+let c2 = db.server1238.find({"loc": {"$within": {"$center": [[5000001, 900000], 5.0]}}}).count();
 
 assert.eq(4, c1, "A1");
 assert.eq(c1, c2, "B1");
diff --git a/jstests/core/index/geo/geo_exactfetch.js b/jstests/core/index/geo/geo_exactfetch.js
index 43ef46fb558..6ced564107f 100644
--- a/jstests/core/index/geo/geo_exactfetch.js
+++ b/jstests/core/index/geo/geo_exactfetch.js
@@ -1,5 +1,5 @@
 // SERVER-7322
-t = db.geo_exactfetch;
+let t = db.geo_exactfetch;
 t.drop();
 
 function test(indexname) {
diff --git a/jstests/core/index/geo/geo_fiddly_box.js b/jstests/core/index/geo/geo_fiddly_box.js
index 9f5a9e8d6c4..84e58aa60e3 100644
--- a/jstests/core/index/geo/geo_fiddly_box.js
+++ b/jstests/core/index/geo/geo_fiddly_box.js
@@ -8,7 +8,7 @@
 // "expand" portion of the geo-lookup expands the 2d range in only one
 // direction (so points are required on either side of the expanding range)
 
-t = db.geo_fiddly_box;
+let t = db.geo_fiddly_box;
 
 t.drop();
 t.createIndex({loc: "2d"});
@@ -28,11 +28,11 @@ assert.eq(
 
 // Test normal lookup of a small square of points as a sanity check.
 
-epsilon = 0.0001;
-min = -1;
-max = 1;
-step = 1;
-numItems = 0;
+let epsilon = 0.0001;
+let min = -1;
+let max = 1;
+let step = 1;
+let numItems = 0;
 
 t.drop();
 t.createIndex({loc: "2d"}, {max: max + epsilon / 2, min: min - epsilon / 2});
diff --git a/jstests/core/index/geo/geo_fiddly_box2.js b/jstests/core/index/geo/geo_fiddly_box2.js
index a0f87203163..c71c4778603 100644
--- a/jstests/core/index/geo/geo_fiddly_box2.js
+++ b/jstests/core/index/geo/geo_fiddly_box2.js
@@ -4,7 +4,7 @@
 // required to do
 // exact lookups on the points to get correct results.
 
-t = db.geo_fiddly_box2;
+let t = db.geo_fiddly_box2;
 t.drop();
 
 t.insert({"letter": "S", "position": [-3, 0]});
@@ -17,7 +17,7 @@ t.insert({"letter": "L", "position": [3, 0]});
 t.insert({"letter": "E", "position": [4, 0]});
 
 t.createIndex({position: "2d"});
-result = t.find({"position": {"$within": {"$box": [[-3, -1], [0, 1]]}}});
+let result = t.find({"position": {"$within": {"$box": [[-3, -1], [0, 1]]}}});
 assert.eq(4, result.count());
 
 t.dropIndex({position: "2d"});
diff --git a/jstests/core/index/geo/geo_invalid_polygon.js b/jstests/core/index/geo/geo_invalid_polygon.js
index 0eab7ca5406..7736f260731 100644
--- a/jstests/core/index/geo/geo_invalid_polygon.js
+++ b/jstests/core/index/geo/geo_invalid_polygon.js
@@ -1,6 +1,6 @@
 // With invalid geometry, error message should include _id
 // SERVER-8992
-t = db.geo_invalid_polygon;
+let t = db.geo_invalid_polygon;
 t.drop();
 
 // Self-intersecting polygon, triggers
diff --git a/jstests/core/index/geo/geo_max.js b/jstests/core/index/geo/geo_max.js
index 3ef6e39dcaa..8db0cbb5858 100644
--- a/jstests/core/index/geo/geo_max.js
+++ b/jstests/core/index/geo/geo_max.js
@@ -16,10 +16,10 @@ test.t.insert({loc: [-180, 0]});
 test.t.insert({loc: [179.999, 0]});
 test.t.insert({loc: [-179.999, 0]});
 
-assertXIsNegative = function(obj) {
+let assertXIsNegative = function(obj) {
     assert.lt(obj.loc[0], 0);
 };
-assertXIsPositive = function(obj) {
+let assertXIsPositive = function(obj) {
     assert.gt(obj.loc[0], 0);
 };
 
diff --git a/jstests/core/index/geo/geo_multikey0.js b/jstests/core/index/geo/geo_multikey0.js
index 27075a779ee..8296dcd6854 100644
--- a/jstests/core/index/geo/geo_multikey0.js
+++ b/jstests/core/index/geo/geo_multikey0.js
@@ -1,6 +1,6 @@
 // Multikey geo values tests - SERVER-3793.
 
-t = db.jstests_geo_multikey0;
+let t = db.jstests_geo_multikey0;
 t.drop();
 
 // Check that conflicting constraints are satisfied by parallel array elements.
diff --git a/jstests/core/index/geo/geo_multikey1.js b/jstests/core/index/geo/geo_multikey1.js
index e6d0ec086da..3bdbea42272 100644
--- a/jstests/core/index/geo/geo_multikey1.js
+++ b/jstests/core/index/geo/geo_multikey1.js
@@ -1,11 +1,11 @@
 // Multikey geo index tests with parallel arrays.
 
-t = db.jstests_geo_multikey1;
+let t = db.jstests_geo_multikey1;
 t.drop();
 
-locArr = [];
-arr = [];
-for (i = 0; i < 10; ++i) {
+let locArr = [];
+let arr = [];
+for (let i = 0; i < 10; ++i) {
     locArr.push([i, i + 1]);
     arr.push(i);
 }
diff --git a/jstests/core/index/geo/geo_multinest0.js b/jstests/core/index/geo/geo_multinest0.js
index 746a530e19b..11111f17a55 100644
--- a/jstests/core/index/geo/geo_multinest0.js
+++ b/jstests/core/index/geo/geo_multinest0.js
@@ -6,7 +6,7 @@
 
 // Make sure nesting of location arrays also works.
 
-t = db.geonest;
+let t = db.geonest;
 t.drop();
 
 t.insert({zip: "10001", data: [{loc: [10, 10], type: "home"}, {loc: [50, 50], type: "work"}]});
diff --git a/jstests/core/index/geo/geo_multinest1.js b/jstests/core/index/geo/geo_multinest1.js
index b6aa53cae16..4cc829e79ba 100644
--- a/jstests/core/index/geo/geo_multinest1.js
+++ b/jstests/core/index/geo/geo_multinest1.js
@@ -6,7 +6,7 @@
 
 // Test distance queries with interleaved distances
 
-t = db.multinest;
+let t = db.multinest;
 t.drop();
 
 t.insert({zip: "10001", data: [{loc: [10, 10], type: "home"}, {loc: [29, 29], type: "work"}]});
diff --git a/jstests/core/index/geo/geo_near_random1.js b/jstests/core/index/geo/geo_near_random1.js
index 1573e72c1f8..b1f5457bdef 100644
--- a/jstests/core/index/geo/geo_near_random1.js
+++ b/jstests/core/index/geo/geo_near_random1.js
@@ -18,9 +18,7 @@ test.testPt(test.mkPt());
 test.testPt(test.mkPt());
 test.testPt(test.mkPt());
 
-opts = {
-    sphere: 1
-};
+let opts = {sphere: 1};
 
 // Test $nearSphere with a 2d index
 test.testPt([0, 0], opts);
diff --git a/jstests/core/index/geo/geo_near_random2.js b/jstests/core/index/geo/geo_near_random2.js
index a9e242edbcc..257b27f4f31 100644
--- a/jstests/core/index/geo/geo_near_random2.js
+++ b/jstests/core/index/geo/geo_near_random2.js
@@ -18,10 +18,7 @@ test.insertPts(5000);
 // distances are in increasing order. The test runs in O(N^2).
 
 // Test $near with 2d index
-opts = {
-    sphere: 0,
-    nToTest: test.nPts * 0.01
-};
+let opts = {sphere: 0, nToTest: test.nPts * 0.01};
 test.testPt([0, 0], opts);
 test.testPt(test.mkPt(), opts);
 test.testPt(test.mkPt(), opts);
diff --git a/jstests/core/index/geo/geo_or.js b/jstests/core/index/geo/geo_or.js
index cee91d4929d..a8fe7ae7b5e 100644
--- a/jstests/core/index/geo/geo_or.js
+++ b/jstests/core/index/geo/geo_or.js
@@ -1,6 +1,6 @@
 // multiple geo clauses with $or
 
-t = db.geoor;
+let t = db.geoor;
 
 t.drop();
 
diff --git a/jstests/core/index/geo/geo_poly_line.js b/jstests/core/index/geo/geo_poly_line.js
index 85dc9274158..58a1ae215f8 100644
--- a/jstests/core/index/geo/geo_poly_line.js
+++ b/jstests/core/index/geo/geo_poly_line.js
@@ -1,6 +1,6 @@
 // Test that weird polygons work SERVER-3725
 
-t = db.geo_polygon5;
+let t = db.geo_polygon5;
 t.drop();
 
 t.insert({loc: [0, 0]});
diff --git a/jstests/core/index/geo/geo_polygon1_noindex.js b/jstests/core/index/geo/geo_polygon1_noindex.js
index 5f43f736b45..8b441c81dc4 100644
--- a/jstests/core/index/geo/geo_polygon1_noindex.js
+++ b/jstests/core/index/geo/geo_polygon1_noindex.js
@@ -1,22 +1,22 @@
 // SERVER-7343: allow $within without a geo index.
 
-t = db.geo_polygon1_noindex;
+let t = db.geo_polygon1_noindex;
 t.drop();
 
-num = 0;
-for (x = 1; x < 9; x++) {
-    for (y = 1; y < 9; y++) {
-        o = {_id: num++, loc: [x, y]};
+let num = 0;
+for (let x = 1; x < 9; x++) {
+    for (let y = 1; y < 9; y++) {
+        let o = {_id: num++, loc: [x, y]};
         t.save(o);
     }
 }
 
-triangle = [[0, 0], [1, 1], [0, 2]];
+let triangle = [[0, 0], [1, 1], [0, 2]];
 
 // Look at only a small slice of the data within a triangle
 assert.eq(1, t.find({loc: {"$within": {"$polygon": triangle}}}).count(), "Triangle Test");
 
-boxBounds = [[0, 0], [0, 10], [10, 10], [10, 0]];
+let boxBounds = [[0, 0], [0, 10], [10, 10], [10, 0]];
 
 assert.eq(num, t.find({loc: {"$within": {"$polygon": boxBounds}}}).count(), "Bounding Box Test");
 
@@ -33,7 +33,7 @@ assert.eq(
 
 t.drop();
 
-pacman = [
+let pacman = [
     [0, 2],
     [0, 4],
     [2, 6],
diff --git a/jstests/core/index/geo/geo_polygon2.js b/jstests/core/index/geo/geo_polygon2.js
index 7a6ad0aedb5..0452b28f563 100644
--- a/jstests/core/index/geo/geo_polygon2.js
+++ b/jstests/core/index/geo/geo_polygon2.js
@@ -29,8 +29,8 @@ for (var test = 0; test < numTests; test++) {
             x = x[0];
         }
 
-        xp = x * Math.cos(rotation) - y * Math.sin(rotation);
-        yp = y * Math.cos(rotation) + x * Math.sin(rotation);
+        let xp = x * Math.cos(rotation) - y * Math.sin(rotation);
+        let yp = y * Math.cos(rotation) + x * Math.sin(rotation);
 
         var scaleX = (bounds[1] - bounds[0]) / 360;
         var scaleY = (bounds[1] - bounds[0]) / 360;
@@ -121,12 +121,13 @@ for (var test = 0; test < numTests; test++) {
         }
     }
 
-    turtlePaths = [];
+    let turtlePaths = [];
     for (var t = 0; t < numTurtles; t++) {
-        turtlePath = [];
+        let turtlePath = [];
 
         var nextSeg = function(currTurtle, prevTurtle) {
             var pathX = currTurtle[0];
+            let pathY;
 
             if (currTurtle[1] < prevTurtle[1]) {
                 pathX = currTurtle[0] + 1;
@@ -150,15 +151,15 @@ for (var test = 0; test < numTests; test++) {
         };
 
         for (var s = 1; s < turtles[t].length; s++) {
-            currTurtle = turtles[t][s];
-            prevTurtle = turtles[t][s - 1];
+            let currTurtle = turtles[t][s];
+            let prevTurtle = turtles[t][s - 1];
 
             turtlePath.push(nextSeg(currTurtle, prevTurtle));
         }
 
         for (var s = turtles[t].length - 2; s >= 0; s--) {
-            currTurtle = turtles[t][s];
-            prevTurtle = turtles[t][s + 1];
+            let currTurtle = turtles[t][s];
+            let prevTurtle = turtles[t][s + 1];
 
             turtlePath.push(nextSeg(currTurtle, prevTurtle));
         }
@@ -169,7 +170,7 @@ for (var test = 0; test < numTests; test++) {
         var lastTurtle = turtles[t][turtles[t].length - 1];
         grid[lastTurtle[0]][lastTurtle[1]] = undefined;
 
-        fixedTurtlePath = [];
+        let fixedTurtlePath = [];
         for (var s = 1; s < turtlePath.length; s++) {
             if (turtlePath[s - 1][0] == turtlePath[s][0] &&
                 turtlePath[s - 1][1] == turtlePath[s][1]) {
@@ -236,7 +237,7 @@ for (var test = 0; test < numTests; test++) {
 
     t.insert({loc: allPointsIn});
     t.insert({loc: allPointsOut});
-    allPoints = allPointsIn.concat(allPointsOut);
+    let allPoints = allPointsIn.concat(allPointsOut);
     t.insert({loc: allPoints});
 
     print("Points : ");
diff --git a/jstests/core/index/geo/geo_queryoptimizer.js b/jstests/core/index/geo/geo_queryoptimizer.js
index 199cedf5330..a9c3378925f 100644
--- a/jstests/core/index/geo/geo_queryoptimizer.js
+++ b/jstests/core/index/geo/geo_queryoptimizer.js
@@ -1,4 +1,4 @@
-t = db.geo_qo1;
+let t = db.geo_qo1;
 t.drop();
 
 t.createIndex({loc: "2d"});
diff --git a/jstests/core/index/geo/geo_regex0.js b/jstests/core/index/geo/geo_regex0.js
index 7629c193ea2..1a7ef2ffde6 100644
--- a/jstests/core/index/geo/geo_regex0.js
+++ b/jstests/core/index/geo/geo_regex0.js
@@ -1,22 +1,15 @@
 // From SERVER-2247
 // Tests to make sure regex works with geo indices
 
-t = db.regex0;
+let t = db.regex0;
 t.drop();
 
 t.createIndex({point: '2d', words: 1});
 t.insert({point: [1, 1], words: ['foo', 'bar']});
 
-regex = {
-    words: /^f/
-};
-geo = {
-    point: {$near: [1, 1]}
-};
-both = {
-    point: {$near: [1, 1]},
-    words: /^f/
-};
+let regex = {words: /^f/};
+let geo = {point: {$near: [1, 1]}};
+let both = {point: {$near: [1, 1]}, words: /^f/};
 
 assert.eq(1, t.find(regex).count());
 assert.eq(1, t.find(geo).count());
diff --git a/jstests/core/index/geo/geo_s2dedupnear.js b/jstests/core/index/geo/geo_s2dedupnear.js
index ad1674f1e6e..89a1c705c71 100644
--- a/jstests/core/index/geo/geo_s2dedupnear.js
+++ b/jstests/core/index/geo/geo_s2dedupnear.js
@@ -1,6 +1,6 @@
 // Make sure that we don't return several of the same result due to faulty
 // assumptions about the btree cursor.  That is, don't return duplicate results.
-t = db.geo_s2dedupnear;
+let t = db.geo_s2dedupnear;
 t.drop();
 
 t.createIndex({geo: "2dsphere"});
@@ -9,5 +9,5 @@ var x = {
     "coordinates": [[[100.0, 0.0], [101.0, 0.0], [101.0, 1.0], [100.0, 1.0], [100.0, 0.0]]]
 };
 t.insert({geo: x});
-res = t.find({geo: {$geoNear: {"type": "Point", "coordinates": [31, 41]}}});
+let res = t.find({geo: {$geoNear: {"type": "Point", "coordinates": [31, 41]}}});
 assert.eq(res.itcount(), 1);
diff --git a/jstests/core/index/geo/geo_s2dupe_points.js b/jstests/core/index/geo/geo_s2dupe_points.js
index 9f94f69caaa..54f9b3b3fc8 100644
--- a/jstests/core/index/geo/geo_s2dupe_points.js
+++ b/jstests/core/index/geo/geo_s2dupe_points.js
@@ -2,7 +2,7 @@
 // s2 rejects shapes with duplicate adjacent points as invalid, but they are
 // valid in GeoJSON.  We store the duplicates, but internally remove them
 // before indexing or querying.
-t = db.geo_s2dupe_points;
+let t = db.geo_s2dupe_points;
 t.drop();
 t.createIndex({geo: "2dsphere"});
 
diff --git a/jstests/core/index/geo/geo_s2edgecases.js b/jstests/core/index/geo/geo_s2edgecases.js
index 6e4633f58c8..b083ea88ae0 100644
--- a/jstests/core/index/geo/geo_s2edgecases.js
+++ b/jstests/core/index/geo/geo_s2edgecases.js
@@ -1,51 +1,42 @@
-t = db.geo_s2edgecases;
+let t = db.geo_s2edgecases;
 t.drop();
 
-roundworldpoint = {
-    "type": "Point",
-    "coordinates": [180, 0]
-};
+let roundworldpoint = {"type": "Point", "coordinates": [180, 0]};
 
 // Opposite the equator
-roundworld = {
+let roundworld = {
     "type": "Polygon",
     "coordinates": [[[179, 1], [-179, 1], [-179, -1], [179, -1], [179, 1]]]
 };
 t.insert({geo: roundworld});
 
-roundworld2 = {
+let roundworld2 = {
     "type": "Polygon",
     "coordinates": [[[179, 1], [179, -1], [-179, -1], [-179, 1], [179, 1]]]
 };
 t.insert({geo: roundworld2});
 
 // North pole
-santapoint = {
-    "type": "Point",
-    "coordinates": [180, 90]
-};
-santa = {
+let santapoint = {"type": "Point", "coordinates": [180, 90]};
+let santa = {
     "type": "Polygon",
     "coordinates": [[[179, 89], [179, 90], [-179, 90], [-179, 89], [179, 89]]]
 };
 t.insert({geo: santa});
-santa2 = {
+let santa2 = {
     "type": "Polygon",
     "coordinates": [[[179, 89], [-179, 89], [-179, 90], [179, 90], [179, 89]]]
 };
 t.insert({geo: santa2});
 
 // South pole
-penguinpoint = {
-    "type": "Point",
-    "coordinates": [0, -90]
-};
-penguin1 = {
+let penguinpoint = {"type": "Point", "coordinates": [0, -90]};
+let penguin1 = {
     "type": "Polygon",
     "coordinates": [[[0, -89], [0, -90], [179, -90], [179, -89], [0, -89]]]
 };
 t.insert({geo: penguin1});
-penguin2 = {
+let penguin2 = {
     "type": "Polygon",
     "coordinates": [[[0, -89], [179, -89], [179, -90], [0, -90], [0, -89]]]
 };
@@ -53,7 +44,7 @@ t.insert({geo: penguin2});
 
 t.createIndex({geo: "2dsphere", nonGeo: 1});
 
-res = t.find({"geo": {"$geoIntersects": {"$geometry": roundworldpoint}}});
+let res = t.find({"geo": {"$geoIntersects": {"$geometry": roundworldpoint}}});
 assert.eq(res.count(), 2);
 res = t.find({"geo": {"$geoIntersects": {"$geometry": santapoint}}});
 assert.eq(res.count(), 2);
diff --git a/jstests/core/index/geo/geo_s2exact.js b/jstests/core/index/geo/geo_s2exact.js
index 92ce551d873..eb563498c07 100644
--- a/jstests/core/index/geo/geo_s2exact.js
+++ b/jstests/core/index/geo/geo_s2exact.js
@@ -1,5 +1,5 @@
 // Queries on exact geometry should return the exact geometry.
-t = db.geo_s2exact;
+let t = db.geo_s2exact;
 t.drop();
 
 function test(geometry) {
@@ -10,20 +10,11 @@ function test(geometry) {
     t.dropIndex({geo: "2dsphere"});
 }
 
-pointA = {
-    "type": "Point",
-    "coordinates": [40, 5]
-};
+let pointA = {"type": "Point", "coordinates": [40, 5]};
 test(pointA);
 
-someline = {
-    "type": "LineString",
-    "coordinates": [[40, 5], [41, 6]]
-};
+let someline = {"type": "LineString", "coordinates": [[40, 5], [41, 6]]};
 test(someline);
 
-somepoly = {
-    "type": "Polygon",
-    "coordinates": [[[40, 5], [40, 6], [41, 6], [41, 5], [40, 5]]]
-};
+let somepoly = {"type": "Polygon", "coordinates": [[[40, 5], [40, 6], [41, 6], [41, 5], [40, 5]]]};
 test(somepoly);
diff --git a/jstests/core/index/geo/geo_s2index.js b/jstests/core/index/geo/geo_s2index.js
index af4475a79cb..9ffdc2c02a0 100644
--- a/jstests/core/index/geo/geo_s2index.js
+++ b/jstests/core/index/geo/geo_s2index.js
@@ -1,56 +1,36 @@
-t = db.geo_s2index;
+let t = db.geo_s2index;
 t.drop();
 
 // We internally drop adjacent duplicate points in lines.
-someline = {
-    "type": "LineString",
-    "coordinates": [[40, 5], [40, 5], [40, 5], [41, 6], [41, 6]]
-};
+let someline = {"type": "LineString", "coordinates": [[40, 5], [40, 5], [40, 5], [41, 6], [41, 6]]};
 t.insert({geo: someline, nonGeo: "someline"});
 t.createIndex({geo: "2dsphere"});
-foo = t.find({geo: {$geoIntersects: {$geometry: {type: "Point", coordinates: [40, 5]}}}}).next();
+let foo =
+    t.find({geo: {$geoIntersects: {$geometry: {type: "Point", coordinates: [40, 5]}}}}).next();
 assert.eq(foo.geo, someline);
 t.dropIndex({geo: "2dsphere"});
 
-pointA = {
-    "type": "Point",
-    "coordinates": [40, 5]
-};
+let pointA = {"type": "Point", "coordinates": [40, 5]};
 t.insert({geo: pointA, nonGeo: "pointA"});
 
-pointD = {
-    "type": "Point",
-    "coordinates": [41.001, 6.001]
-};
+let pointD = {"type": "Point", "coordinates": [41.001, 6.001]};
 t.insert({geo: pointD, nonGeo: "pointD"});
 
-pointB = {
-    "type": "Point",
-    "coordinates": [41, 6]
-};
+let pointB = {"type": "Point", "coordinates": [41, 6]};
 t.insert({geo: pointB, nonGeo: "pointB"});
 
-pointC = {
-    "type": "Point",
-    "coordinates": [41, 6]
-};
+let pointC = {"type": "Point", "coordinates": [41, 6]};
 t.insert({geo: pointC});
 
 // Add a point within the polygon but not on the border.  Don't want to be on
 // the path of the polyline.
-pointE = {
-    "type": "Point",
-    "coordinates": [40.6, 5.4]
-};
+let pointE = {"type": "Point", "coordinates": [40.6, 5.4]};
 t.insert({geo: pointE});
 
 // Make sure we can index this without error.
 t.insert({nonGeo: "noGeoField!"});
 
-somepoly = {
-    "type": "Polygon",
-    "coordinates": [[[40, 5], [40, 6], [41, 6], [41, 5], [40, 5]]]
-};
+let somepoly = {"type": "Polygon", "coordinates": [[[40, 5], [40, 6], [41, 6], [41, 5], [40, 5]]]};
 t.insert({geo: somepoly, nonGeo: "somepoly"});
 
 var res = t.createIndex({geo: "2dsphere", nonGeo: 1});
diff --git a/jstests/core/index/geo/geo_s2indexoldformat.js b/jstests/core/index/geo/geo_s2indexoldformat.js
index ffe472464d4..ad1008115dd 100644
--- a/jstests/core/index/geo/geo_s2indexoldformat.js
+++ b/jstests/core/index/geo/geo_s2indexoldformat.js
@@ -1,6 +1,6 @@
 // Make sure that the 2dsphere index can deal with non-GeoJSON points.
 // 2dsphere does not accept legacy shapes, only legacy points.
-t = db.geo_s2indexoldformat;
+let t = db.geo_s2indexoldformat;
 t.drop();
 
 t.insert({geo: [40, 5], nonGeo: ["pointA"]});
@@ -11,7 +11,7 @@ t.insert({geo: {x: 40.6, y: 5.4}});
 
 t.createIndex({geo: "2dsphere", nonGeo: 1});
 
-res = t.find({"geo": {"$geoIntersects": {"$geometry": {x: 40, y: 5}}}});
+let res = t.find({"geo": {"$geoIntersects": {"$geometry": {x: 40, y: 5}}}});
 assert.eq(res.count(), 1);
 
 res = t.find({"geo": {"$geoIntersects": {"$geometry": [41, 6]}}});
diff --git a/jstests/core/index/geo/geo_s2largewithin.js b/jstests/core/index/geo/geo_s2largewithin.js
index e1eed8a2e6a..d94ebc5f0a7 100644
--- a/jstests/core/index/geo/geo_s2largewithin.js
+++ b/jstests/core/index/geo/geo_s2largewithin.js
@@ -1,20 +1,17 @@
 // If our $within is enormous, create a coarse covering for the search so it
 // doesn't take forever.
-t = db.geo_s2largewithin;
+let t = db.geo_s2largewithin;
 t.drop();
 t.createIndex({geo: "2dsphere"});
 
-testPoint = {
-    name: "origin",
-    geo: {type: "Point", coordinates: [0.0, 0.0]}
-};
+let testPoint = {name: "origin", geo: {type: "Point", coordinates: [0.0, 0.0]}};
 
-testHorizLine = {
+let testHorizLine = {
     name: "horiz",
     geo: {type: "LineString", coordinates: [[-2.0, 10.0], [2.0, 10.0]]}
 };
 
-testVertLine = {
+let testVertLine = {
     name: "vert",
     geo: {type: "LineString", coordinates: [[10.0, -2.0], [10.0, 2.0]]}
 };
@@ -25,12 +22,12 @@ t.insert(testVertLine);
 
 // Test a poly that runs horizontally along the equator.
 
-longPoly = {
+let longPoly = {
     type: "Polygon",
     coordinates: [[[30.0, 1.0], [-30.0, 1.0], [-30.0, -1.0], [30.0, -1.0], [30.0, 1.0]]]
 };
 
-result = t.find({geo: {$geoWithin: {$geometry: longPoly}}});
+let result = t.find({geo: {$geoWithin: {$geometry: longPoly}}});
 assert.eq(result.itcount(), 1);
 result = t.find({geo: {$geoWithin: {$geometry: longPoly}}});
 assert.eq("origin", result[0].name);
diff --git a/jstests/core/index/geo/geo_s2meridian.js b/jstests/core/index/geo/geo_s2meridian.js
index 99eb0c63dc4..a0196bb5a41 100644
--- a/jstests/core/index/geo/geo_s2meridian.js
+++ b/jstests/core/index/geo/geo_s2meridian.js
@@ -1,4 +1,4 @@
-t = db.geo_s2meridian;
+let t = db.geo_s2meridian;
 t.drop();
 t.createIndex({geo: "2dsphere"});
 
@@ -8,18 +8,15 @@ t.createIndex({geo: "2dsphere"});
  * that runs along the meridian.
  */
 
-meridianCrossingLine = {
+let meridianCrossingLine = {
     geo: {type: "LineString", coordinates: [[-178.0, 10.0], [178.0, 10.0]]}
 };
 
 assert.commandWorked(t.insert(meridianCrossingLine));
 
-lineAlongMeridian = {
-    type: "LineString",
-    coordinates: [[180.0, 11.0], [180.0, 9.0]]
-};
+let lineAlongMeridian = {type: "LineString", coordinates: [[180.0, 11.0], [180.0, 9.0]]};
 
-result = t.find({geo: {$geoIntersects: {$geometry: lineAlongMeridian}}});
+let result = t.find({geo: {$geoIntersects: {$geometry: lineAlongMeridian}}});
 assert.eq(result.itcount(), 1);
 
 t.drop();
@@ -29,21 +26,15 @@ t.createIndex({geo: "2dsphere"});
  * on the meridian, and immediately on either side, and confirm that a poly
  * covering all of them returns them all.
  */
-pointOnNegativeSideOfMeridian = {
-    geo: {type: "Point", coordinates: [-179.0, 1.0]}
-};
-pointOnMeridian = {
-    geo: {type: "Point", coordinates: [180.0, 1.0]}
-};
-pointOnPositiveSideOfMeridian = {
-    geo: {type: "Point", coordinates: [179.0, 1.0]}
-};
+let pointOnNegativeSideOfMeridian = {geo: {type: "Point", coordinates: [-179.0, 1.0]}};
+let pointOnMeridian = {geo: {type: "Point", coordinates: [180.0, 1.0]}};
+let pointOnPositiveSideOfMeridian = {geo: {type: "Point", coordinates: [179.0, 1.0]}};
 
 t.insert(pointOnMeridian);
 t.insert(pointOnNegativeSideOfMeridian);
 t.insert(pointOnPositiveSideOfMeridian);
 
-meridianCrossingPoly = {
+let meridianCrossingPoly = {
     type: "Polygon",
     coordinates: [[[-178.0, 10.0], [178.0, 10.0], [178.0, -10.0], [-178.0, -10.0], [-178.0, 10.0]]]
 };
@@ -58,15 +49,9 @@ t.createIndex({geo: "2dsphere"});
  * closer, but across the meridian, and confirm they both come back, and
  * that the order is correct.
  */
-pointOnNegativeSideOfMerid = {
-    name: "closer",
-    geo: {type: "Point", coordinates: [-179.0, 0.0]}
-};
+let pointOnNegativeSideOfMerid = {name: "closer", geo: {type: "Point", coordinates: [-179.0, 0.0]}};
 
-pointOnPositiveSideOfMerid = {
-    name: "farther",
-    geo: {type: "Point", coordinates: [176.0, 0.0]}
-};
+let pointOnPositiveSideOfMerid = {name: "farther", geo: {type: "Point", coordinates: [176.0, 0.0]}};
 
 t.insert(pointOnNegativeSideOfMerid);
 t.insert(pointOnPositiveSideOfMerid);
diff --git a/jstests/core/index/geo/geo_s2multi.js b/jstests/core/index/geo/geo_s2multi.js
index 858dfd1efa1..3da229ad743 100644
--- a/jstests/core/index/geo/geo_s2multi.js
+++ b/jstests/core/index/geo/geo_s2multi.js
@@ -1,22 +1,19 @@
-t = db.geo_s2multi;
+let t = db.geo_s2multi;
 t.drop();
 
 t.createIndex({geo: "2dsphere"});
 
 // Let's try the examples in the GeoJSON spec.
-multiPointA = {
-    "type": "MultiPoint",
-    "coordinates": [[100.0, 0.0], [101.0, 1.0]]
-};
+let multiPointA = {"type": "MultiPoint", "coordinates": [[100.0, 0.0], [101.0, 1.0]]};
 assert.commandWorked(t.insert({geo: multiPointA}));
 
-multiLineStringA = {
+let multiLineStringA = {
     "type": "MultiLineString",
     "coordinates": [[[100.0, 0.0], [101.0, 1.0]], [[102.0, 2.0], [103.0, 3.0]]]
 };
 assert.commandWorked(t.insert({geo: multiLineStringA}));
 
-multiPolygonA = {
+let multiPolygonA = {
     "type": "MultiPolygon",
     "coordinates": [
         [[[102.0, 2.0], [103.0, 2.0], [103.0, 3.0], [102.0, 3.0], [102.0, 2.0]]],
@@ -61,7 +58,7 @@ assert.eq(
 // Polygon contains itself and the multipoint.
 assert.eq(2, t.find({geo: {$geoWithin: {$geometry: multiPolygonA}}}).itcount());
 
-partialPolygonA = {
+let partialPolygonA = {
     "type": "Polygon",
     "coordinates": [[[102.0, 2.0], [103.0, 2.0], [103.0, 3.0], [102.0, 3.0], [102.0, 2.0]]]
 };
diff --git a/jstests/core/index/geo/geo_s2near.js b/jstests/core/index/geo/geo_s2near.js
index 2cd732da67a..7c584992e8a 100644
--- a/jstests/core/index/geo/geo_s2near.js
+++ b/jstests/core/index/geo/geo_s2near.js
@@ -4,17 +4,14 @@
 
 // Test 2dsphere near search, called via find and $geoNear.
 (function() {
-t = db.geo_s2near;
+let t = db.geo_s2near;
 t.drop();
 
 // Make sure that geoNear gives us back loc
-goldenPoint = {
-    type: "Point",
-    coordinates: [31.0, 41.0]
-};
+let goldenPoint = {type: "Point", coordinates: [31.0, 41.0]};
 t.insert({geo: goldenPoint});
 t.createIndex({geo: "2dsphere"});
-resNear =
+let resNear =
     t.aggregate([
          {$geoNear: {near: [30, 40], distanceField: "d", spherical: true, includeLocs: "loc"}},
          {$limit: 1}
@@ -25,31 +22,22 @@ assert.eq(resNear[0].loc, goldenPoint);
 // FYI:
 // One degree of long @ 0 is 111km or so.
 // One degree of lat @ 0 is 110km or so.
-lat = 0;
-lng = 0;
-points = 10;
+let lat = 0;
+let lng = 0;
+let points = 10;
 for (var x = -points; x < points; x += 1) {
     for (var y = -points; y < points; y += 1) {
         t.insert({geo: {"type": "Point", "coordinates": [lng + x / 1000.0, lat + y / 1000.0]}});
     }
 }
 
-origin = {
-    "type": "Point",
-    "coordinates": [lng, lat]
-};
+let origin = {"type": "Point", "coordinates": [lng, lat]};
 
 t.createIndex({geo: "2dsphere"});
 
 // Near only works when the query is a point.
-someline = {
-    "type": "LineString",
-    "coordinates": [[40, 5], [41, 6]]
-};
-somepoly = {
-    "type": "Polygon",
-    "coordinates": [[[40, 5], [40, 6], [41, 6], [41, 5], [40, 5]]]
-};
+let someline = {"type": "LineString", "coordinates": [[40, 5], [41, 6]]};
+let somepoly = {"type": "Polygon", "coordinates": [[[40, 5], [40, 6], [41, 6], [41, 5], [40, 5]]]};
 assert.throws(function() {
     return t.find({"geo": {"$near": {"$geometry": someline}}}).count();
 });
@@ -70,7 +58,7 @@ assert.commandFailedWithCode(db.runCommand({
                              2);
 
 // Do some basic near searches.
-res = t.find({"geo": {"$near": {"$geometry": origin, $maxDistance: 2000}}}).limit(10);
+let res = t.find({"geo": {"$near": {"$geometry": origin, $maxDistance: 2000}}}).limit(10);
 resNear = t.aggregate([
     {$geoNear: {near: [0, 0], distanceField: "dis", maxDistance: Math.PI, spherical: true}},
     {$limit: 10},
@@ -109,29 +97,30 @@ assert.eq(res.itcount(), resNear.itcount(), ((2 * points) * (2 * points) + 4).to
 
 function testRadAndDegreesOK(distance) {
     // Distance for old style points is radians.
-    resRadians = t.find({geo: {$nearSphere: [0, 0], $maxDistance: (distance / (6378.1 * 1000))}});
+    let resRadians =
+        t.find({geo: {$nearSphere: [0, 0], $maxDistance: (distance / (6378.1 * 1000))}});
     // Distance for new style points is meters.
-    resMeters = t.find({"geo": {"$near": {"$geometry": origin, $maxDistance: distance}}});
+    let resMeters = t.find({"geo": {"$near": {"$geometry": origin, $maxDistance: distance}}});
     // And we should get the same # of results no matter what.
     assert.eq(resRadians.itcount(), resMeters.itcount());
 
     // Also, $geoNear should behave the same way.
-    resGNMeters = t.aggregate({
-                       $geoNear: {
-                           near: origin,
-                           distanceField: "dis",
-                           maxDistance: distance,
-                           spherical: true,
-                       }
-                   }).toArray();
-    resGNRadians = t.aggregate({
-                        $geoNear: {
-                            near: [0, 0],
-                            distanceField: "dis",
-                            maxDistance: (distance / (6378.1 * 1000)),
-                            spherical: true,
-                        }
-                    }).toArray();
+    let resGNMeters = t.aggregate({
+                           $geoNear: {
+                               near: origin,
+                               distanceField: "dis",
+                               maxDistance: distance,
+                               spherical: true,
+                           }
+                       }).toArray();
+    let resGNRadians = t.aggregate({
+                            $geoNear: {
+                                near: [0, 0],
+                                distanceField: "dis",
+                                maxDistance: (distance / (6378.1 * 1000)),
+                                spherical: true,
+                            }
+                        }).toArray();
     const errmsg = `$geoNear using meter distances returned ${tojson(resGNMeters)}, but ` +
         `$geoNear using radian distances returned ${tojson(resGNRadians)}`;
     assert.eq(resGNRadians.length, resGNMeters.length, errmsg);
diff --git a/jstests/core/index/geo/geo_s2nearComplex.js b/jstests/core/index/geo/geo_s2nearComplex.js
index 22fe3112499..df978d45e61 100644
--- a/jstests/core/index/geo/geo_s2nearComplex.js
+++ b/jstests/core/index/geo/geo_s2nearComplex.js
@@ -18,7 +18,7 @@ var atan2 = Math.atan2;
 
 var originGeo = {type: "Point", coordinates: [20.0, 20.0]};
 // Center point for all tests.
-var origin = {name: "origin", geo: originGeo};
+let origin = {name: "origin", geo: originGeo};
 
 /*
  * Convenience function for checking that coordinates match.  threshold let's you
@@ -114,7 +114,7 @@ function uniformPointsWithClusters(
     origin, count, minDist, maxDist, numberOfClusters, minClusterSize, maxClusterSize, distRatio) {
     distRatio = distRatio || 10;
     var points = uniformPoints(origin, count, minDist, maxDist);
-    for (j = 0; j < numberOfClusters; j++) {
+    for (let j = 0; j < numberOfClusters; j++) {
         var randomPoint = points[Math.floor(random() * points.length)];
         var clusterSize = (random() * (maxClusterSize - minClusterSize)) + minClusterSize;
         uniformPoints(randomPoint, clusterSize, minDist / distRatio, maxDist / distRatio);
@@ -146,18 +146,18 @@ function validateOrdering(query) {
     var near30 = t.find(query).limit(30);
     var near40 = t.find(query).limit(40);
 
-    for (i = 0; i < 10; i++) {
+    for (let i = 0; i < 10; i++) {
         assert(coordinateEqual(near10[i], near20[i]));
         assert(coordinateEqual(near10[i], near30[i]));
         assert(coordinateEqual(near10[i], near40[i]));
     }
 
-    for (i = 0; i < 20; i++) {
+    for (let i = 0; i < 20; i++) {
         assert(coordinateEqual(near20[i], near30[i]));
         assert(coordinateEqual(near20[i], near40[i]));
     }
 
-    for (i = 0; i < 30; i++) {
+    for (let i = 0; i < 30; i++) {
         assert(coordinateEqual(near30[i], near40[i]));
     }
 }
@@ -281,7 +281,7 @@ origin = {
 
 uniformPoints(origin, 10, 89, 90);
 
-cur = t.find({geo: {$near: {$geometry: originGeo}}});
+let cur = t.find({geo: {$near: {$geometry: originGeo}}});
 
 assert.eq(cur.itcount(), 10);
 cur = t.find({geo: {$near: {$geometry: originGeo}}});
@@ -290,5 +290,5 @@ print("Near search on very distant points:");
 print(t.find({geo: {$geoNear: {$geometry: originGeo}}})
           .explain("executionStats")
           .executionStats.executionTimeMillis);
-pt = cur.next();
+let pt = cur.next();
 assert(pt);
diff --git a/jstests/core/index/geo/geo_s2nearcorrect.js b/jstests/core/index/geo/geo_s2nearcorrect.js
index 80ece4223d2..b21782140be 100644
--- a/jstests/core/index/geo/geo_s2nearcorrect.js
+++ b/jstests/core/index/geo/geo_s2nearcorrect.js
@@ -2,17 +2,11 @@
 // A geometry may have several covers, one of which is in a search ring and the other of which is
 // not.  If we see the cover that's not in the search ring, we can't mark the object as 'seen' for
 // this ring.
-t = db.geo_s2nearcorrect;
+let t = db.geo_s2nearcorrect;
 t.drop();
 
-longline = {
-    "type": "LineString",
-    "coordinates": [[0, 0], [179, 89]]
-};
+let longline = {"type": "LineString", "coordinates": [[0, 0], [179, 89]]};
 t.insert({geo: longline});
 t.createIndex({geo: "2dsphere"});
-origin = {
-    "type": "Point",
-    "coordinates": [45, 45]
-};
+let origin = {"type": "Point", "coordinates": [45, 45]};
 assert.eq(1, t.find({"geo": {"$near": {"$geometry": origin, $maxDistance: 20000000}}}).count());
diff --git a/jstests/core/index/geo/geo_s2nongeoarray.js b/jstests/core/index/geo/geo_s2nongeoarray.js
index f5830e8702d..3e2b0d5eb52 100644
--- a/jstests/core/index/geo/geo_s2nongeoarray.js
+++ b/jstests/core/index/geo/geo_s2nongeoarray.js
@@ -1,8 +1,8 @@
 // Explode arrays when indexing non-geo fields in 2dsphere, and make sure that
 // we find them with queries.
-t = db.geo_s2nongeoarray;
+let t = db.geo_s2nongeoarray;
 
-oldPoint = [40, 5];
+let oldPoint = [40, 5];
 
 var data = {geo: oldPoint, nonGeo: [123, 456], otherNonGeo: [{b: [1, 2]}, {b: [3, 4]}]};
 
diff --git a/jstests/core/index/geo/geo_s2nonstring.js b/jstests/core/index/geo/geo_s2nonstring.js
index a76a7cd073e..b7f9496a3b9 100644
--- a/jstests/core/index/geo/geo_s2nonstring.js
+++ b/jstests/core/index/geo/geo_s2nonstring.js
@@ -1,5 +1,5 @@
 // Added to make sure that S2 indexing's string AND non-string keys work.
-t = db.geo_s2nonstring;
+let t = db.geo_s2nonstring;
 t.drop();
 
 t.createIndex({geo: '2dsphere', x: 1});
diff --git a/jstests/core/index/geo/geo_s2nopoints.js b/jstests/core/index/geo/geo_s2nopoints.js
index 7b3a3b970a7..b27c2ea2034 100644
--- a/jstests/core/index/geo/geo_s2nopoints.js
+++ b/jstests/core/index/geo/geo_s2nopoints.js
@@ -1,5 +1,5 @@
 // See SERVER-7794.
-t = db.geo_s2nopoints;
+let t = db.geo_s2nopoints;
 t.drop();
 
 t.createIndex({loc: "2dsphere", x: 1});
diff --git a/jstests/core/index/geo/geo_s2oddshapes.js b/jstests/core/index/geo/geo_s2oddshapes.js
index db30d431caa..e6610dea12a 100644
--- a/jstests/core/index/geo/geo_s2oddshapes.js
+++ b/jstests/core/index/geo/geo_s2oddshapes.js
@@ -96,7 +96,7 @@ outsidePoint = {
 t.insert(insidePoint);
 t.insert(outsidePoint);
 
-smallPoly = {
+let smallPoly = {
     type: "Polygon",
     coordinates: [[[0.0, -0.01], [0.015, -0.01], [0.015, 0.01], [0.0, 0.01], [0.0, -0.01]]]
 };
diff --git a/jstests/core/index/geo/geo_s2twofields.js b/jstests/core/index/geo/geo_s2twofields.js
index 9f769f6897f..af7f07f64eb 100644
--- a/jstests/core/index/geo/geo_s2twofields.js
+++ b/jstests/core/index/geo/geo_s2twofields.js
@@ -33,7 +33,7 @@ for (var i = 0; i < maxPoints; ++i) {
     arr.push(
         {from: {type: "Point", coordinates: fromCoord}, to: {type: "Point", coordinates: toCoord}});
 }
-res = t.insert(arr);
+let res = t.insert(arr);
 assert.commandWorked(res);
 assert.eq(t.count(), maxPoints);
 
diff --git a/jstests/core/index/geo/geo_s2within.js b/jstests/core/index/geo/geo_s2within.js
index 04915c77dcb..6950cb3e482 100644
--- a/jstests/core/index/geo/geo_s2within.js
+++ b/jstests/core/index/geo/geo_s2within.js
@@ -1,18 +1,15 @@
 // Test some cases that might be iffy with $within, mostly related to polygon w/holes.
-t = db.geo_s2within;
+let t = db.geo_s2within;
 t.drop();
 t.createIndex({geo: "2dsphere"});
 
-somepoly = {
-    "type": "Polygon",
-    "coordinates": [[[40, 5], [40, 6], [41, 6], [41, 5], [40, 5]]]
-};
+let somepoly = {"type": "Polygon", "coordinates": [[[40, 5], [40, 6], [41, 6], [41, 5], [40, 5]]]};
 
 t.insert({geo: {"type": "LineString", "coordinates": [[40.1, 5.1], [40.2, 5.2]]}});
 // This is only partially contained within the polygon.
 t.insert({geo: {"type": "LineString", "coordinates": [[40.1, 5.1], [42, 7]]}});
 
-res = t.find({"geo": {"$within": {"$geometry": somepoly}}});
+let res = t.find({"geo": {"$within": {"$geometry": somepoly}}});
 assert.eq(res.itcount(), 1);
 
 t.drop();
diff --git a/jstests/core/index/geo/geo_sort1.js b/jstests/core/index/geo/geo_sort1.js
index 4d32c2f4ae2..5f90ea50d60 100644
--- a/jstests/core/index/geo/geo_sort1.js
+++ b/jstests/core/index/geo/geo_sort1.js
@@ -1,21 +1,21 @@
-t = db.geo_sort1;
+let t = db.geo_sort1;
 t.drop();
 
-for (x = 0; x < 10; x++) {
-    for (y = 0; y < 10; y++) {
+for (let x = 0; x < 10; x++) {
+    for (let y = 0; y < 10; y++) {
         t.insert({loc: [x, y], foo: x * x * y});
     }
 }
 
 t.createIndex({loc: "2d", foo: 1});
 
-q = t.find({loc: {$near: [5, 5]}, foo: {$gt: 20}});
-m = function(z) {
+let q = t.find({loc: {$near: [5, 5]}, foo: {$gt: 20}});
+let m = function(z) {
     return z.foo;
 };
 
-a = q.clone().map(m);
-b = q.clone().sort({foo: 1}).map(m);
+let a = q.clone().map(m);
+let b = q.clone().sort({foo: 1}).map(m);
 
 assert.neq(a, b, "A");
 a.sort();
diff --git a/jstests/core/index/geo/geo_uniqueDocs.js b/jstests/core/index/geo/geo_uniqueDocs.js
index 9e0a811e7e7..418f48691ed 100644
--- a/jstests/core/index/geo/geo_uniqueDocs.js
+++ b/jstests/core/index/geo/geo_uniqueDocs.js
@@ -1,8 +1,8 @@
 // Test uniqueDocs option for $within queries and the $geoNear aggregation stage. SERVER-3139
 // SERVER-12120 uniqueDocs is deprecated. Server always returns unique documents.
 
-collName = 'geo_uniqueDocs_test';
-t = db.geo_uniqueDocs_test;
+let collName = 'geo_uniqueDocs_test';
+let t = db.geo_uniqueDocs_test;
 t.drop();
 
 assert.commandWorked(t.save({locs: [[0, 2], [3, 4]]}));
@@ -21,7 +21,8 @@ assert.eq(2,
           t.aggregate({$geoNear: {near: [0, 0], distanceField: "dis", uniqueDocs: true}})
               .toArray()
               .length);
-results = t.aggregate([{$geoNear: {near: [0, 0], distanceField: "dis"}}, {$limit: 2}]).toArray();
+let results =
+    t.aggregate([{$geoNear: {near: [0, 0], distanceField: "dis"}}, {$limit: 2}]).toArray();
 assert.eq(2, results.length);
 assert.close(2, results[0].dis);
 assert.close(10, results[1].dis);
diff --git a/jstests/core/index/geo/geo_update1.js b/jstests/core/index/geo/geo_update1.js
index f982966afd7..67b40a66ffb 100644
--- a/jstests/core/index/geo/geo_update1.js
+++ b/jstests/core/index/geo/geo_update1.js
@@ -3,7 +3,7 @@
 //   requires_non_retryable_writes,
 // ]
 
-t = db.geo_update1;
+let t = db.geo_update1;
 t.drop();
 
 for (var x = 0; x < 10; x++) {
diff --git a/jstests/core/index/geo/geo_update2.js b/jstests/core/index/geo/geo_update2.js
index 280023ffe44..4073a5ccd9c 100644
--- a/jstests/core/index/geo/geo_update2.js
+++ b/jstests/core/index/geo/geo_update2.js
@@ -3,7 +3,7 @@
 //   requires_non_retryable_writes,
 // ]
 
-t = db.geo_update2;
+let t = db.geo_update2;
 t.drop();
 
 for (var x = 0; x < 10; x++) {
diff --git a/jstests/core/index/geo/geo_update_btree.js b/jstests/core/index/geo/geo_update_btree.js
index 7a58362fe18..403af8e5f0c 100644
--- a/jstests/core/index/geo/geo_update_btree.js
+++ b/jstests/core/index/geo/geo_update_btree.js
@@ -27,7 +27,7 @@ var parallelInsert = startParallelShell(
     "    db.jstests_geo_update_btree.insert(doc);" +
     "}");
 
-for (i = 0; i < 1000; i++) {
+for (let i = 0; i < 1000; i++) {
     coll.update({
         loc: {$within: {$center: [[Random.rand() * 180, Random.rand() * 180], Random.rand() * 50]}}
     },
diff --git a/jstests/core/index/geo/geo_withinquery.js b/jstests/core/index/geo/geo_withinquery.js
index 13f20c1433f..c4069d93f4d 100644
--- a/jstests/core/index/geo/geo_withinquery.js
+++ b/jstests/core/index/geo/geo_withinquery.js
@@ -3,13 +3,13 @@
 // ]
 
 // SERVER-7343: allow $within without a geo index.
-t = db.geo_withinquery;
+let t = db.geo_withinquery;
 t.drop();
 
-num = 0;
-for (x = 0; x <= 20; x++) {
-    for (y = 0; y <= 20; y++) {
-        o = {_id: num++, loc: [x, y]};
+let num = 0;
+for (let x = 0; x <= 20; x++) {
+    for (let y = 0; y <= 20; y++) {
+        let o = {_id: num++, loc: [x, y]};
         t.save(o);
     }
 }
diff --git a/jstests/core/index/geo/geoa.js b/jstests/core/index/geo/geoa.js
index 78cf6c960c9..26bfc10b8cf 100644
--- a/jstests/core/index/geo/geoa.js
+++ b/jstests/core/index/geo/geoa.js
@@ -1,4 +1,4 @@
-t = db.geoa;
+let t = db.geoa;
 t.drop();
 
 t.save({_id: 1, a: {loc: [5, 5]}});
@@ -7,5 +7,5 @@ t.save({_id: 3, a: {loc: [7, 7]}});
 
 t.createIndex({"a.loc": "2d"});
 
-cur = t.find({"a.loc": {$near: [6, 6]}});
+let cur = t.find({"a.loc": {$near: [6, 6]}});
 assert.eq(2, cur.next()._id, "A1");
diff --git a/jstests/core/index/geo/geoc.js b/jstests/core/index/geo/geoc.js
index 8875cd44614..5d8752b95a3 100644
--- a/jstests/core/index/geo/geoc.js
+++ b/jstests/core/index/geo/geoc.js
@@ -2,10 +2,10 @@
 //   requires_getmore,
 // ]
 
-t = db.geoc;
+let t = db.geoc;
 t.drop();
 
-N = 1000;
+let N = 1000;
 
 for (var i = 0; i < N; i++)
     t.insert({loc: [100 + Math.random(), 100 + Math.random()], z: 0});
diff --git a/jstests/core/index/geo/geod.js b/jstests/core/index/geo/geod.js
index 8586d64e398..27272929f65 100644
--- a/jstests/core/index/geo/geod.js
+++ b/jstests/core/index/geo/geod.js
@@ -5,13 +5,13 @@ t.save({loc: [0.5, 0]});
 t.createIndex({loc: "2d"});
 // do a few geoNears with different maxDistances.  The first iteration
 // should match no points in the dataset.
-dists = [.49, .51, 1.0];
-for (idx in dists) {
-    b = db.geod
-            .aggregate([
-                {$geoNear: {near: [1, 0], distanceField: "d", maxDistance: dists[idx]}},
-                {$limit: 2},
-            ])
-            .toArray();
+let dists = [.49, .51, 1.0];
+for (let idx in dists) {
+    let b = db.geod
+                .aggregate([
+                    {$geoNear: {near: [1, 0], distanceField: "d", maxDistance: dists[idx]}},
+                    {$limit: 2},
+                ])
+                .toArray();
     assert.eq(b.length, idx, "B" + idx);
 }
diff --git a/jstests/core/index/geo/geoe.js b/jstests/core/index/geo/geoe.js
index 84bc34f7a74..eac049e0574 100644
--- a/jstests/core/index/geo/geoe.js
+++ b/jstests/core/index/geo/geoe.js
@@ -4,7 +4,7 @@
 // the end of the btree and not reverse direction (leaving the rest of
 // the search always looking at some random non-matching point).
 
-t = db.geo_box;
+let t = db.geo_box;
 t.drop();
 
 t.insert({"_id": 1, "geo": [33, -11.1]});
@@ -24,7 +24,7 @@ t.insert({"_id": 14, "geo": [-122.289505, 37.695774]});
 
 t.createIndex({geo: "2d"});
 
-c = t.find({geo: {"$within": {"$box": [[-125.078461, 36.494473], [-120.320648, 38.905199]]}}});
+let c = t.find({geo: {"$within": {"$box": [[-125.078461, 36.494473], [-120.320648, 38.905199]]}}});
 assert.eq(11, c.count(), "A1");
 
 c = t.find({geo: {"$within": {"$box": [[-124.078461, 36.494473], [-120.320648, 38.905199]]}}});
diff --git a/jstests/core/index/geo/geof.js b/jstests/core/index/geo/geof.js
index 1f1d9e0cc67..8dce3f68b6f 100644
--- a/jstests/core/index/geo/geof.js
+++ b/jstests/core/index/geo/geof.js
@@ -1,4 +1,4 @@
-t = db.geof;
+let t = db.geof;
 t.drop();
 
 // corners (dist ~0.98)
diff --git a/jstests/core/index/index1.js b/jstests/core/index/index1.js
index 4c06bfe03fd..e3805a6d4e8 100644
--- a/jstests/core/index/index1.js
+++ b/jstests/core/index/index1.js
@@ -1,13 +1,10 @@
 // @tags: [requires_non_retryable_writes]
 
-t = db.embeddedIndexTest;
+let t = db.embeddedIndexTest;
 
 t.remove({});
 
-o = {
-    name: "foo",
-    z: {a: 17, b: 4}
-};
+let o = {name: "foo", z: {a: 17, b: 4}};
 t.save(o);
 
 assert(t.findOne().z.a == 17);
diff --git a/jstests/core/index/index13.js b/jstests/core/index/index13.js
index 97a3a85f773..ff2cb55332e 100644
--- a/jstests/core/index/index13.js
+++ b/jstests/core/index/index13.js
@@ -21,7 +21,7 @@
 // SERVER-3104 implementation, the index constraints become [3,3] on the 'a.b' field _and_ [3,3] on
 // the 'a.c' field.
 
-t = db.jstests_index13;
+let t = db.jstests_index13;
 t.drop();
 
 function assertConsistentResults(query) {
@@ -30,16 +30,13 @@ function assertConsistentResults(query) {
 }
 
 function assertResults(query) {
-    explain = t.find(query).hint(index).explain();
+    let explain = t.find(query).hint(index).explain();
     // printjson( explain ); // debug
     assertConsistentResults(query);
 }
 
 // Cases with single dotted index fied names.
-index = {
-    'a.b': 1,
-    'a.c': 1
-};
+let index = {'a.b': 1, 'a.c': 1};
 t.createIndex(index);
 t.save({a: [{b: 1}, {c: 1}]});
 t.save({a: [{b: 1, c: 1}]});
diff --git a/jstests/core/index/index4.js b/jstests/core/index/index4.js
index 179bcdd9726..d5771862131 100644
--- a/jstests/core/index/index4.js
+++ b/jstests/core/index/index4.js
@@ -6,7 +6,7 @@
 
 // index4.js
 
-t = db.index4;
+let t = db.index4;
 t.drop();
 
 t.save({name: "alleyinsider", instances: [{pool: "prod1"}, {pool: "dev1"}]});
@@ -21,7 +21,7 @@ t.createIndex({"instances.pool": 1});
 
 sleep(10);
 
-a = t.find({instances: {pool: "prod1"}});
+let a = t.find({instances: {pool: "prod1"}});
 assert(a.length() == 1, "len1");
 assert(a[0].name == "alleyinsider", "alley");
 
diff --git a/jstests/core/index/index5.js b/jstests/core/index/index5.js
index 908b433c299..8175d5bcc54 100644
--- a/jstests/core/index/index5.js
+++ b/jstests/core/index/index5.js
@@ -4,17 +4,17 @@
 
 function validate() {
     assert.eq(2, t.find().count());
-    f = t.find().sort({a: 1});
+    let f = t.find().sort({a: 1});
     assert.eq(2, t.count());
     assert.eq(1, f[0].a);
     assert.eq(2, f[1].a);
-    r = t.find().sort({a: -1});
+    let r = t.find().sort({a: -1});
     assert.eq(2, r.count());
     assert.eq(2, r[0].a);
     assert.eq(1, r[1].a);
 }
 
-t = db.index5;
+let t = db.index5;
 t.drop();
 
 t.save({a: 1});
diff --git a/jstests/core/index/index6.js b/jstests/core/index/index6.js
index 4626e9359ea..3edefedfc1b 100644
--- a/jstests/core/index/index6.js
+++ b/jstests/core/index/index6.js
@@ -1,6 +1,6 @@
 // index6.js Test indexes on array subelements.
 
-r = db.ed.db.index6;
+let r = db.ed.db.index6;
 r.drop();
 
 r.save({comments: [{name: "eliot", foo: 1}]});
diff --git a/jstests/core/index/index8.js b/jstests/core/index/index8.js
index 3887906dddc..2b62040ca50 100644
--- a/jstests/core/index/index8.js
+++ b/jstests/core/index/index8.js
@@ -12,14 +12,14 @@
 // Test key uniqueness
 (function() {
 
-t = db.jstests_index8;
+let t = db.jstests_index8;
 t.drop();
 
 t.createIndex({a: 1});
 t.createIndex({b: 1}, true);
 t.createIndex({c: 1}, [false, "cIndex"]);
 
-checkIndexes = function(num) {
+let checkIndexes = function(num) {
     const indexes = t.getIndexes();
     assert.eq(4, indexes.length);
 
diff --git a/jstests/core/index/index9.js b/jstests/core/index/index9.js
index 7bf7ec5ac43..ed7da662858 100644
--- a/jstests/core/index/index9.js
+++ b/jstests/core/index/index9.js
@@ -2,7 +2,7 @@
 // expected.  Also, the primary node cannot change because we use the local database in this test.
 // @tags: [assumes_no_implicit_collection_creation_after_drop, does_not_support_stepdowns]
 
-t = db.jstests_index9;
+let t = db.jstests_index9;
 
 t.drop();
 assert.commandWorked(db.createCollection("jstests_index9"));
diff --git a/jstests/core/index/index_arr1.js b/jstests/core/index/index_arr1.js
index d6db3e621cd..749b54543d5 100644
--- a/jstests/core/index/index_arr1.js
+++ b/jstests/core/index/index_arr1.js
@@ -2,7 +2,7 @@
 // collection.
 // @tags: [assumes_no_implicit_index_creation]
 
-t = db.index_arr1;
+let t = db.index_arr1;
 t.drop();
 
 t.insert({_id: 1, a: 5, b: [{x: 1}]});
diff --git a/jstests/core/index/index_arr2.js b/jstests/core/index/index_arr2.js
index 99950880422..ae977f5a514 100644
--- a/jstests/core/index/index_arr2.js
+++ b/jstests/core/index/index_arr2.js
@@ -1,27 +1,27 @@
 // @tags: [assumes_balancer_off, requires_multi_updates, requires_non_retryable_writes]
 
-NUM = 20;
-M = 5;
+let NUM = 20;
+let M = 5;
 
-t = db.jstests_arr2;
+let t = db.jstests_arr2;
 
 function test(withIndex) {
     t.drop();
 
     // insert a bunch of items to force queries to use the index.
-    newObject = {_id: 1, a: [{b: {c: 1}}]};
+    let newObject = {_id: 1, a: [{b: {c: 1}}]};
 
-    now = (new Date()).getTime() / 1000;
-    for (created = now - NUM; created <= now; created++) {
+    let now = (new Date()).getTime() / 1000;
+    for (let created = now - NUM; created <= now; created++) {
         newObject['created'] = created;
         t.insert(newObject);
         newObject['_id']++;
     }
 
     // change the last M items.
-    query = {'created': {'$gte': now - M}};
+    let query = {'created': {'$gte': now - M}};
 
-    Z = t.find(query).count();
+    let Z = t.find(query).count();
 
     if (withIndex) {
         // t.createIndex( { 'a.b.c' : 1, 'created' : -1 } )
@@ -35,7 +35,7 @@ function test(withIndex) {
     // now see how many were actually updated.
     query['a.b.c'] = 0;
 
-    count = t.count(query);
+    let count = t.count(query);
 
     assert.eq(Z, count, "count after withIndex:" + withIndex);
 }
diff --git a/jstests/core/index/index_bounds_number_edge_cases.js b/jstests/core/index/index_bounds_number_edge_cases.js
index 3da4e53e2d0..6f08c663246 100644
--- a/jstests/core/index/index_bounds_number_edge_cases.js
+++ b/jstests/core/index/index_bounds_number_edge_cases.js
@@ -2,7 +2,7 @@
 // should handle numerical extremes
 // such as Number.MAX_VALUE and Infinity
 
-t = db.indexboundsnumberedgecases;
+let t = db.indexboundsnumberedgecases;
 
 t.drop();
 
diff --git a/jstests/core/index/index_check2.js b/jstests/core/index/index_check2.js
index e296e3b558a..170c54a0322 100644
--- a/jstests/core/index/index_check2.js
+++ b/jstests/core/index/index_check2.js
@@ -3,7 +3,7 @@
 //   requires_getmore
 // ]
 
-t = db.index_check2;
+let t = db.index_check2;
 t.drop();
 
 // Include helpers for analyzing explain output.
@@ -17,15 +17,9 @@ for (var i = 0; i < 1000; i++) {
     t.save({num: i, tags: a});
 }
 
-q1 = {
-    tags: "tag6"
-};
-q2 = {
-    tags: "tag12"
-};
-q3 = {
-    tags: {$all: ["tag6", "tag12"]}
-};
+let q1 = {tags: "tag6"};
+let q2 = {tags: "tag12"};
+let q3 = {tags: {$all: ["tag6", "tag12"]}};
 
 assert.eq(120, t.find(q1).itcount(), "q1 a");
 assert.eq(120, t.find(q2).itcount(), "q2 a");
@@ -42,9 +36,9 @@ assert(isIxscan(db, getWinningPlan(t.find(q1).explain().queryPlanner)), "e1");
 assert(isIxscan(db, getWinningPlan(t.find(q2).explain().queryPlanner)), "e2");
 assert(isIxscan(db, getWinningPlan(t.find(q3).explain().queryPlanner)), "e3");
 
-scanned1 = t.find(q1).explain("executionStats").executionStats.totalKeysExamined;
-scanned2 = t.find(q2).explain("executionStats").executionStats.totalKeysExamined;
-scanned3 = t.find(q3).explain("executionStats").executionStats.totalKeysExamined;
+let scanned1 = t.find(q1).explain("executionStats").executionStats.totalKeysExamined;
+let scanned2 = t.find(q2).explain("executionStats").executionStats.totalKeysExamined;
+let scanned3 = t.find(q3).explain("executionStats").executionStats.totalKeysExamined;
 
 // print( "scanned1: " + scanned1 + " scanned2: " + scanned2 + " scanned3: " + scanned3 );
 
diff --git a/jstests/core/index/index_check5.js b/jstests/core/index/index_check5.js
index 8921e014fcd..62f72c0e612 100644
--- a/jstests/core/index/index_check5.js
+++ b/jstests/core/index/index_check5.js
@@ -1,5 +1,5 @@
 
-t = db.index_check5;
+let t = db.index_check5;
 t.drop();
 
 t.save({
diff --git a/jstests/core/index/index_diag.js b/jstests/core/index/index_diag.js
index 769e5575bf1..bb9cd4ed323 100644
--- a/jstests/core/index/index_diag.js
+++ b/jstests/core/index/index_diag.js
@@ -3,14 +3,14 @@
 // ]
 load("jstests/libs/fixture_helpers.js");
 
-t = db.index_diag;
+let t = db.index_diag;
 t.drop();
 
 assert.commandWorked(t.createIndex({x: 1}));
 
-all = [];
-ids = [];
-xs = [];
+let all = [];
+let ids = [];
+let xs = [];
 
 function r(a) {
     var n = [];
@@ -19,8 +19,8 @@ function r(a) {
     return n;
 }
 
-for (i = 1; i < 4; i++) {
-    o = {_id: i, x: -i};
+for (let i = 1; i < 4; i++) {
+    let o = {_id: i, x: -i};
     t.insert(o);
     all.push(o);
     ids.push({_id: i});
diff --git a/jstests/core/index/index_filter_commands.js b/jstests/core/index/index_filter_commands.js
index 429a79adea8..dd60bfbc18c 100644
--- a/jstests/core/index/index_filter_commands.js
+++ b/jstests/core/index/index_filter_commands.js
@@ -187,7 +187,7 @@ assert.eq(null, planCacheEntryForQuery(shape), coll.getPlanCache().list());
 
 // Check details of winning plan in plan cache after setting filter and re-executing query.
 assert.eq(1, coll.find(queryA1, projectionA1).sort(sortA1).itcount(), 'unexpected document count');
-planAfterSetFilter = planCacheEntryForQuery(shape);
+let planAfterSetFilter = planCacheEntryForQuery(shape);
 assert.neq(null, planAfterSetFilter, coll.getPlanCache().list());
 // Check 'indexFilterSet' field in plan details
 assert.eq(true, planAfterSetFilter.indexFilterSet, planAfterSetFilter);
@@ -441,7 +441,7 @@ if (checkSBEEnabled(db)) {
     assert.eq(lookupStage.strategy, "IndexedLoopJoin", explain);
     assert.eq(lookupStage.indexName, "foreign_a_1");
 
-    ixscanStage = getPlanStage(explain, "IXSCAN");
+    let ixscanStage = getPlanStage(explain, "IXSCAN");
     assert.neq(null, ixscanStage, explain);
     assert.eq(ixscanStage.indexName, "main_a_1_c_1", explain);
 
diff --git a/jstests/core/index/index_many.js b/jstests/core/index/index_many.js
index cdd559c9be5..ee1f71477c0 100644
--- a/jstests/core/index/index_many.js
+++ b/jstests/core/index/index_many.js
@@ -4,7 +4,7 @@
 
 /* test using lots of indexes on one collection */
 
-t = db.many;
+let t = db.many;
 
 function f() {
     t.drop();
@@ -13,10 +13,10 @@ function f() {
     t.save({x: 9, y: 99});
     t.save({x: 19, y: 99});
 
-    x = 2;
+    let x = 2;
     var lastErr = null;
     while (x < 70) {
-        patt = {};
+        let patt = {};
         patt[x] = 1;
         if (x == 20)
             patt = {x: 1};
@@ -29,7 +29,7 @@ function f() {
     assert.commandFailed(lastErr, "should have got an error 'too many indexes'");
 
     // 40 is the limit currently
-    lim = t.getIndexes().length;
+    let lim = t.getIndexes().length;
     if (lim != 64) {
         print("# of indexes should be 64 but is : " + lim);
         return;
diff --git a/jstests/core/index/index_sparse1.js b/jstests/core/index/index_sparse1.js
index 58bc5baa9b8..0aec94e8ab2 100644
--- a/jstests/core/index/index_sparse1.js
+++ b/jstests/core/index/index_sparse1.js
@@ -2,7 +2,7 @@
 // collection.
 // @tags: [assumes_no_implicit_index_creation, requires_non_retryable_writes, requires_fastcount]
 
-t = db.index_sparse1;
+let t = db.index_sparse1;
 t.drop();
 
 t.insert({_id: 1, x: 1});
diff --git a/jstests/core/index/index_sparse2.js b/jstests/core/index/index_sparse2.js
index 324b46d8216..c7a9b0fac04 100644
--- a/jstests/core/index/index_sparse2.js
+++ b/jstests/core/index/index_sparse2.js
@@ -2,7 +2,7 @@
 // collection.
 // @tags: [assumes_no_implicit_index_creation, requires_fastcount]
 
-t = db.index_sparse2;
+let t = db.index_sparse2;
 t.drop();
 
 t.insert({_id: 1, x: 1, y: 1});
diff --git a/jstests/core/index/indexa.js b/jstests/core/index/indexa.js
index 01fde035621..937dde52df1 100644
--- a/jstests/core/index/indexa.js
+++ b/jstests/core/index/indexa.js
@@ -5,7 +5,7 @@
 // unique index constraint test for updates
 // case where object doesn't grow tested here
 
-t = db.indexa;
+let t = db.indexa;
 t.drop();
 
 t.createIndex({x: 1}, true);
@@ -18,8 +18,8 @@ assert.eq(2, t.count(), "indexa 1");
 
 t.update({x: 'B'}, {x: 'A'});
 
-a = t.find().toArray();
-u = Array.unique(a.map(function(z) {
+let a = t.find().toArray();
+let u = Array.unique(a.map(function(z) {
     return z.x;
 }));
 assert.eq(2, t.count(), "indexa 2");
diff --git a/jstests/core/index/indexb.js b/jstests/core/index/indexb.js
index 59546f7fae2..5c5177fd239 100644
--- a/jstests/core/index/indexb.js
+++ b/jstests/core/index/indexb.js
@@ -8,15 +8,13 @@
 // see indexa.js for the test case for an update with dup id check
 // when it doesn't move
 
-t = db.indexb;
+let t = db.indexb;
 t.drop();
 t.createIndex({a: 1}, true);
 
 t.insert({a: 1});
 
-x = {
-    a: 2
-};
+let x = {a: 2};
 t.save(x);
 
 {
diff --git a/jstests/core/index/indexc.js b/jstests/core/index/indexc.js
index bf5735380fa..b65d5a6e891 100644
--- a/jstests/core/index/indexc.js
+++ b/jstests/core/index/indexc.js
@@ -1,5 +1,5 @@
 
-t = db.indexc;
+let t = db.indexc;
 t.drop();
 
 const startMillis = new Date().getTime();
@@ -7,7 +7,7 @@ for (var i = 1; i < 100; i++) {
     var d = new Date(startMillis + i);
     t.save({a: i, ts: d, cats: [i, i + 1, i + 2]});
     if (i == 51)
-        mid = d;
+        var mid = d;
 }
 
 assert.eq(50, t.find({ts: {$lt: mid}}).itcount(), "A");
diff --git a/jstests/core/index/indexe.js b/jstests/core/index/indexe.js
index a307882adc3..aaafc5bda3b 100644
--- a/jstests/core/index/indexe.js
+++ b/jstests/core/index/indexe.js
@@ -1,11 +1,11 @@
 // @tags: [requires_getmore, requires_fastcount]
 
-t = db.indexe;
+let t = db.indexe;
 t.drop();
 
 var num = 1000;
 
-for (i = 0; i < num; i++) {
+for (let i = 0; i < num; i++) {
     t.insert({a: "b"});
 }
 
diff --git a/jstests/core/index/indexf.js b/jstests/core/index/indexf.js
index 37c27967229..8837b9e2571 100644
--- a/jstests/core/index/indexf.js
+++ b/jstests/core/index/indexf.js
@@ -1,5 +1,5 @@
 
-t = db.indexf;
+let t = db.indexf;
 t.drop();
 
 t.createIndex({x: 1});
diff --git a/jstests/core/index/indexg.js b/jstests/core/index/indexg.js
index f8f466d6495..47f7a587d9e 100644
--- a/jstests/core/index/indexg.js
+++ b/jstests/core/index/indexg.js
@@ -1,10 +1,10 @@
 
-f = db.jstests_indexg;
+let f = db.jstests_indexg;
 f.drop();
 f.save({list: [1, 2]});
 f.save({list: [1, 3]});
 
-doit = function() {
+let doit = function() {
     assert.eq(1, f.count({list: {$in: [1], $ne: 3}}));
     assert.eq(1, f.count({list: {$in: [1], $not: {$in: [3]}}}));
 };
diff --git a/jstests/core/index/indexl.js b/jstests/core/index/indexl.js
index d372c770574..d0ba873e437 100644
--- a/jstests/core/index/indexl.js
+++ b/jstests/core/index/indexl.js
@@ -1,6 +1,6 @@
 // Check nonoverlapping $in/$all with multikeys SERVER-2165
 
-t = db.jstests_indexl;
+let t = db.jstests_indexl;
 
 function test(t) {
     t.save({a: [1, 2]});
diff --git a/jstests/core/index/indexm.js b/jstests/core/index/indexm.js
index 7613b125357..2fc04263273 100644
--- a/jstests/core/index/indexm.js
+++ b/jstests/core/index/indexm.js
@@ -1,6 +1,6 @@
 // Check proper range combinations with or clauses overlapping non or portion of query SERVER-2302
 
-t = db.jstests_indexm;
+let t = db.jstests_indexm;
 t.drop();
 
 t.save({a: [{x: 1}, {x: 2}, {x: 3}, {x: 4}]});
diff --git a/jstests/core/index/indexn.js b/jstests/core/index/indexn.js
index a292ae2e5d3..ddd7dc5169d 100644
--- a/jstests/core/index/indexn.js
+++ b/jstests/core/index/indexn.js
@@ -4,7 +4,7 @@
 //   assumes_read_concern_local,
 // ]
 
-t = db.jstests_indexn;
+let t = db.jstests_indexn;
 t.drop();
 
 t.save({a: 1, b: [1, 2]});
diff --git a/jstests/core/index/indexr.js b/jstests/core/index/indexr.js
index d3ff5f7e02e..a056d29281f 100644
--- a/jstests/core/index/indexr.js
+++ b/jstests/core/index/indexr.js
@@ -4,7 +4,7 @@
 
 // Check multikey index cases with parallel nested fields SERVER-958.
 
-t = db.jstests_indexr;
+let t = db.jstests_indexr;
 t.drop();
 
 // Check without indexes.
diff --git a/jstests/core/index/indexs.js b/jstests/core/index/indexs.js
index 6ee625071e2..6cbabbb8f82 100644
--- a/jstests/core/index/indexs.js
+++ b/jstests/core/index/indexs.js
@@ -1,7 +1,7 @@
 // Test index key generation issue with parent and nested fields in same index and array containing
 // subobject SERVER-3005.
 
-t = db.jstests_indexs;
+let t = db.jstests_indexs;
 
 t.drop();
 t.createIndex({a: 1});
diff --git a/jstests/core/index/indext.js b/jstests/core/index/indext.js
index 1ac92d6be5d..13e0ce0fb57 100644
--- a/jstests/core/index/indext.js
+++ b/jstests/core/index/indext.js
@@ -1,6 +1,6 @@
 // Sparse indexes with arrays SERVER-3216
 
-t = db.jstests_indext;
+let t = db.jstests_indext;
 t.drop();
 
 t.createIndex({'a.b': 1}, {sparse: true});
diff --git a/jstests/core/index/useindexonobjgtlt.js b/jstests/core/index/useindexonobjgtlt.js
index 506618e16c6..bcdf36f3279 100644
--- a/jstests/core/index/useindexonobjgtlt.js
+++ b/jstests/core/index/useindexonobjgtlt.js
@@ -1,6 +1,6 @@
 // @tags: [requires_fastcount]
 
-t = db.factories;
+let t = db.factories;
 t.drop();
 t.insert({name: "xyz", metro: {city: "New York", state: "NY"}});
 t.createIndex({metro: 1});
diff --git a/jstests/core/index/wildcard/compound_wildcard_index_hiding.js b/jstests/core/index/wildcard/compound_wildcard_index_hiding.js
index a3e304bfc4b..903624d4273 100644
--- a/jstests/core/index/wildcard/compound_wildcard_index_hiding.js
+++ b/jstests/core/index/wildcard/compound_wildcard_index_hiding.js
@@ -51,17 +51,6 @@ const cwiList = [
     },
 ];
 
-function validateIndex(coll, indexSpec) {
-    const index = findIndex(coll, indexSpec);
-    assert.neq(null, index);
-
-    if (indexSpec.hidden) {
-        assert.eq(true, index.hidden);
-    } else {
-        assert.neq(true, index.hidden);
-    }
-}
-
 function setIndexVisibilityByKeyPattern(collectionName, keyPattern, hidden) {
     assert.commandWorked(db.runCommand({collMod: collectionName, index: {keyPattern, hidden}}));
 }
diff --git a/jstests/core/json1.js b/jstests/core/json1.js
index 31b2794c9a9..fdcea151e05 100644
--- a/jstests/core/json1.js
+++ b/jstests/core/json1.js
@@ -1,8 +1,5 @@
 
-x = {
-    quotes: "a\"b",
-    nulls: null
-};
+let x = {quotes: "a\"b", nulls: null};
 eval("y = " + tojson(x));
 assert.eq(tojson(x), tojson(y), "A");
 assert.eq(typeof (x.nulls), typeof (y.nulls), "B");
diff --git a/jstests/core/json_schema/misc_validation.js b/jstests/core/json_schema/misc_validation.js
index 4821c0643f9..76dec255711 100644
--- a/jstests/core/json_schema/misc_validation.js
+++ b/jstests/core/json_schema/misc_validation.js
@@ -38,8 +38,6 @@ assert.commandWorked(testDB.createCollection(testName));
 const coll = testDB.getCollection(testName);
 coll.drop();
 
-const isMongos = (testDB.runCommand("hello").msg === "isdbgrid");
-
 // Test that $jsonSchema is rejected in an $elemMatch projection.
 assert.throws(function() {
     coll.find({}, {a: {$elemMatch: {$jsonSchema: {}}}}).itcount();
diff --git a/jstests/core/jssymbol.js b/jstests/core/jssymbol.js
index 714ea48870a..9465b6774c0 100644
--- a/jstests/core/jssymbol.js
+++ b/jstests/core/jssymbol.js
@@ -16,9 +16,9 @@ assert(db[Symbol.species] != 1);
 assert(db[Symbol.toPrimitive] != 1);
 
 // Exercise Symbol.toPrimitive on BSON objects
-col1 = db.jssymbol_col;
+let col1 = db.jssymbol_col;
 col1.insert({});
-a = db.getCollection("jssymbol_col").getIndexes()[0];
+let a = db.getCollection("jssymbol_col").getIndexes()[0];
 
 assert(isNaN(+a));
 assert(+a.v >= 1);
diff --git a/jstests/core/logprocessdetails.js b/jstests/core/logprocessdetails.js
index 4c72f802262..fe9c8a99b1c 100644
--- a/jstests/core/logprocessdetails.js
+++ b/jstests/core/logprocessdetails.js
@@ -14,7 +14,7 @@
  * Checks an array for match against regex.
  * Returns true if regex matches a string in the array
  */
-doesLogMatchRegex = function(logArray, regex) {
+let doesLogMatchRegex = function(logArray, regex) {
     for (var i = (logArray.length - 1); i >= 0; i--) {
         var regexInLine = regex.exec(logArray[i]);
         if (regexInLine != null) {
@@ -24,7 +24,7 @@ doesLogMatchRegex = function(logArray, regex) {
     return false;
 };
 
-doTest = function() {
+let doTest = function() {
     var log = db.adminCommand({getLog: 'global'});
     // this regex will need to change if output changes
     var re = new RegExp(".*conn.*options.*");
diff --git a/jstests/core/multi.js b/jstests/core/multi.js
index ac961ed7a9c..58cb327f86f 100644
--- a/jstests/core/multi.js
+++ b/jstests/core/multi.js
@@ -1,4 +1,4 @@
-t = db.jstests_multi;
+let t = db.jstests_multi;
 t.drop();
 
 t.createIndex({a: 1});
diff --git a/jstests/core/multi2.js b/jstests/core/multi2.js
index 64473e4de98..cf9dd924d51 100644
--- a/jstests/core/multi2.js
+++ b/jstests/core/multi2.js
@@ -1,6 +1,6 @@
 // @tags: [requires_fastcount]
 
-t = db.multi2;
+let t = db.multi2;
 t.drop();
 
 t.save({x: 1, a: [1]});
diff --git a/jstests/core/notablescan.js b/jstests/core/notablescan.js
index f9addc78099..ff9a0b91f2d 100644
--- a/jstests/core/notablescan.js
+++ b/jstests/core/notablescan.js
@@ -16,7 +16,7 @@
 //   tenant_migration_incompatible,
 // ]
 
-t = db.test_notablescan;
+let t = db.test_notablescan;
 t.drop();
 
 try {
diff --git a/jstests/core/notablescan_capped.js b/jstests/core/notablescan_capped.js
index cc7405ff88b..43ac4d43f94 100644
--- a/jstests/core/notablescan_capped.js
+++ b/jstests/core/notablescan_capped.js
@@ -17,14 +17,14 @@
 //   tenant_migration_incompatible,
 // ]
 
-t = db.test_notablescan_capped;
+let t = db.test_notablescan_capped;
 t.drop();
 assert.commandWorked(db.createCollection(t.getName(), {capped: true, size: 100}));
 
 try {
     assert.commandWorked(db._adminCommand({setParameter: 1, notablescan: true}));
 
-    err = assert.throws(function() {
+    let err = assert.throws(function() {
         t.find({a: 1}).tailable(true).next();
     });
     assert.includes(err.toString(), "tailable");
diff --git a/jstests/core/operation_latency_histogram.js b/jstests/core/operation_latency_histogram.js
index cd220deae48..703d5da8f6b 100644
--- a/jstests/core/operation_latency_histogram.js
+++ b/jstests/core/operation_latency_histogram.js
@@ -27,6 +27,7 @@
 (function() {
 "use strict";
 
+load("jstests/libs/fixture_helpers.js");
 load("jstests/libs/stats.js");
 var name = "operationalLatencyHistogramTest";
 
@@ -145,8 +146,7 @@ lastHistogram = assertHistogramDiffEq(testColl, lastHistogram, 0, 0, 1);
 
 // Reindex (Only standalone mode supports the reIndex command.)
 const hello = db.runCommand({hello: 1});
-const isMongos = (hello.msg === "isdbgrid");
-const isStandalone = !isMongos && !hello.hasOwnProperty('setName');
+const isStandalone = !FixtureHelpers.isMongos(db) && !hello.hasOwnProperty('setName');
 if (isStandalone) {
     assert.commandWorked(testColl.reIndex());
     lastHistogram = assertHistogramDiffEq(testColl, lastHistogram, 0, 0, 1);
diff --git a/jstests/core/query/all/all.js b/jstests/core/query/all/all.js
index a718e2615e8..9132c6f7c51 100644
--- a/jstests/core/query/all/all.js
+++ b/jstests/core/query/all/all.js
@@ -1,7 +1,7 @@
-t = db.jstests_all;
+let t = db.jstests_all;
 t.drop();
 
-doTest = function() {
+let doTest = function() {
     assert.commandWorked(t.save({a: [1, 2, 3]}));
     assert.commandWorked(t.save({a: [1, 2, 4]}));
     assert.commandWorked(t.save({a: [1, 8, 5]}));
diff --git a/jstests/core/query/all/all2.js b/jstests/core/query/all/all2.js
index b0c6d40cf68..738b5f746d0 100644
--- a/jstests/core/query/all/all2.js
+++ b/jstests/core/query/all/all2.js
@@ -1,11 +1,11 @@
-t = db.all2;
+let t = db.all2;
 t.drop();
 
 t.save({a: [{x: 1}, {x: 2}]});
 t.save({a: [{x: 2}, {x: 3}]});
 t.save({a: [{x: 3}, {x: 4}]});
 
-state = "no index";
+let state = "no index";
 
 function check(n, q, e) {
     assert.eq(n, t.find(q).count(), tojson(q) + " " + e + " count " + state);
diff --git a/jstests/core/query/all/all3.js b/jstests/core/query/all/all3.js
index 37cb6c690b2..ee14e3a1102 100644
--- a/jstests/core/query/all/all3.js
+++ b/jstests/core/query/all/all3.js
@@ -2,7 +2,7 @@
 
 // Check that $all matching null is consistent with $in - SERVER-3820
 
-t = db.jstests_all3;
+let t = db.jstests_all3;
 t.drop();
 
 t.save({});
diff --git a/jstests/core/query/all/all4.js b/jstests/core/query/all/all4.js
index eb979289496..d3486b467ad 100644
--- a/jstests/core/query/all/all4.js
+++ b/jstests/core/query/all/all4.js
@@ -1,6 +1,6 @@
 // Test $all/$elemMatch with missing field - SERVER-4492
 
-t = db.jstests_all4;
+let t = db.jstests_all4;
 t.drop();
 
 function checkQuery(query, val) {
diff --git a/jstests/core/query/all/all5.js b/jstests/core/query/all/all5.js
index a5faaa1767f..ff14671d524 100644
--- a/jstests/core/query/all/all5.js
+++ b/jstests/core/query/all/all5.js
@@ -1,6 +1,6 @@
 // Test $all/$elemMatch/null matching - SERVER-4517
 
-t = db.jstests_all5;
+let t = db.jstests_all5;
 t.drop();
 
 function checkMatch(doc) {
diff --git a/jstests/core/query/and/and.js b/jstests/core/query/and/and.js
index 20fd583c31f..c68f8381886 100644
--- a/jstests/core/query/and/and.js
+++ b/jstests/core/query/and/and.js
@@ -4,7 +4,7 @@
 //     requires_scripting
 // ]
 
-t = db.jstests_and;
+let t = db.jstests_and;
 t.drop();
 
 t.save({a: [1, 2]});
diff --git a/jstests/core/query/and/and2.js b/jstests/core/query/and/and2.js
index 5a946c2cb76..79d4fc590c4 100644
--- a/jstests/core/query/and/and2.js
+++ b/jstests/core/query/and/and2.js
@@ -5,7 +5,7 @@
 
 // Test dollar sign operator with $and SERVER-1089
 
-t = db.jstests_and2;
+let t = db.jstests_and2;
 
 t.drop();
 t.save({a: [1, 2]});
diff --git a/jstests/core/query/and/and3.js b/jstests/core/query/and/and3.js
index 5256237bc33..1dfecc87ffa 100644
--- a/jstests/core/query/and/and3.js
+++ b/jstests/core/query/and/and3.js
@@ -6,7 +6,7 @@
 //   assumes_read_concern_local,
 // ]
 
-t = db.jstests_and3;
+let t = db.jstests_and3;
 t.drop();
 
 t.save({a: 1});
diff --git a/jstests/core/query/and/andor.js b/jstests/core/query/and/andor.js
index 5bac12d83ca..b8ae2df86a9 100644
--- a/jstests/core/query/and/andor.js
+++ b/jstests/core/query/and/andor.js
@@ -1,6 +1,6 @@
 // SERVER-1089 Test and/or/nor nesting
 
-t = db.jstests_andor;
+let t = db.jstests_andor;
 t.drop();
 
 // not ok
@@ -10,7 +10,7 @@ function ok(q) {
 
 t.save({a: 1});
 
-test = function() {
+let test = function() {
     ok({a: 1});
 
     ok({$and: [{a: 1}]});
diff --git a/jstests/core/query/array/array3.js b/jstests/core/query/array/array3.js
index 42acdfb6d3e..16d03b880ed 100644
--- a/jstests/core/query/array/array3.js
+++ b/jstests/core/query/array/array3.js
@@ -2,6 +2,6 @@
 assert.eq(5, Array.sum([1, 4]), "A");
 assert.eq(2.5, Array.avg([1, 4]), "B");
 
-arr = [2, 4, 4, 4, 5, 5, 7, 9];
+let arr = [2, 4, 4, 4, 5, 5, 7, 9];
 assert.eq(5, Array.avg(arr), "C");
 assert.eq(2, Array.stdDev(arr), "D");
diff --git a/jstests/core/query/array/array_match1.js b/jstests/core/query/array/array_match1.js
index 0c56e8d4c34..e21d0a9e7c9 100644
--- a/jstests/core/query/array/array_match1.js
+++ b/jstests/core/query/array/array_match1.js
@@ -1,4 +1,4 @@
-t = db.array_match1;
+let t = db.array_match1;
 t.drop();
 
 t.insert({_id: 1, a: [5, 5]});
diff --git a/jstests/core/query/array/array_match2.js b/jstests/core/query/array/array_match2.js
index 3e0dde8f5f5..fa4034d5c3c 100644
--- a/jstests/core/query/array/array_match2.js
+++ b/jstests/core/query/array/array_match2.js
@@ -1,6 +1,6 @@
 // @tags: [requires_non_retryable_writes]
 
-t = db.jstests_array_match2;
+let t = db.jstests_array_match2;
 t.drop();
 
 t.save({a: [{1: 4}, 5]});
diff --git a/jstests/core/query/array/array_match3.js b/jstests/core/query/array/array_match3.js
index 4990bdd90fd..ad362e5e43b 100644
--- a/jstests/core/query/array/array_match3.js
+++ b/jstests/core/query/array/array_match3.js
@@ -1,6 +1,6 @@
 // SERVER-2902 Test indexing of numerically referenced array elements.
 
-t = db.jstests_array_match3;
+let t = db.jstests_array_match3;
 t.drop();
 
 // Test matching numericallly referenced array element.
diff --git a/jstests/core/query/array/arrayfind1.js b/jstests/core/query/array/arrayfind1.js
index 4e9330549ae..b50ecae7809 100644
--- a/jstests/core/query/array/arrayfind1.js
+++ b/jstests/core/query/array/arrayfind1.js
@@ -2,7 +2,7 @@
 //   requires_fastcount,
 // ]
 
-t = db.arrayfind1;
+let t = db.arrayfind1;
 t.drop();
 
 t.save({a: [{x: 1}]});
diff --git a/jstests/core/query/array/arrayfind2.js b/jstests/core/query/array/arrayfind2.js
index 38de844f6f4..14eb2411e7c 100644
--- a/jstests/core/query/array/arrayfind2.js
+++ b/jstests/core/query/array/arrayfind2.js
@@ -1,6 +1,6 @@
 // @tags: [requires_fastcount]
 
-t = db.arrayfind2;
+let t = db.arrayfind2;
 t.drop();
 
 function go(prefix) {
diff --git a/jstests/core/query/array/arrayfind3.js b/jstests/core/query/array/arrayfind3.js
index 6dba0bf625f..619ed2e1046 100644
--- a/jstests/core/query/array/arrayfind3.js
+++ b/jstests/core/query/array/arrayfind3.js
@@ -1,4 +1,4 @@
-t = db.arrayfind3;
+let t = db.arrayfind3;
 t.drop();
 
 t.save({a: [1, 2]});
diff --git a/jstests/core/query/array/arrayfind4.js b/jstests/core/query/array/arrayfind4.js
index 2d7c0e03668..231abee50dd 100644
--- a/jstests/core/query/array/arrayfind4.js
+++ b/jstests/core/query/array/arrayfind4.js
@@ -4,7 +4,7 @@
 
 // Test query empty array SERVER-2258
 
-t = db.jstests_arrayfind4;
+let t = db.jstests_arrayfind4;
 t.drop();
 
 t.save({a: []});
diff --git a/jstests/core/query/array/arrayfind5.js b/jstests/core/query/array/arrayfind5.js
index 004231e0893..6238284f89a 100644
--- a/jstests/core/query/array/arrayfind5.js
+++ b/jstests/core/query/array/arrayfind5.js
@@ -4,7 +4,7 @@
 //   cqf_incompatible,
 // ]
 
-t = db.jstests_arrayfind5;
+let t = db.jstests_arrayfind5;
 t.drop();
 
 function check(nullElemMatch) {
diff --git a/jstests/core/query/array/arrayfind6.js b/jstests/core/query/array/arrayfind6.js
index bd91859c9dc..2788fa6d07e 100644
--- a/jstests/core/query/array/arrayfind6.js
+++ b/jstests/core/query/array/arrayfind6.js
@@ -1,6 +1,6 @@
 // Check index bound determination for $not:$elemMatch queries.  SERVER-5740
 
-t = db.jstests_arrayfind6;
+let t = db.jstests_arrayfind6;
 t.drop();
 
 t.save({a: [{b: 1, c: 2}]});
diff --git a/jstests/core/query/array/arrayfind7.js b/jstests/core/query/array/arrayfind7.js
index be2061c5c0d..2d3fe471797 100644
--- a/jstests/core/query/array/arrayfind7.js
+++ b/jstests/core/query/array/arrayfind7.js
@@ -1,6 +1,6 @@
 // Nested $elemMatch clauses.  SERVER-5741
 
-t = db.jstests_arrayfind7;
+let t = db.jstests_arrayfind7;
 t.drop();
 
 t.save({a: [{b: [{c: 1, d: 2}]}]});
diff --git a/jstests/core/query/array/arrayfind9.js b/jstests/core/query/array/arrayfind9.js
index 5406ae8c1d1..88a781e9999 100644
--- a/jstests/core/query/array/arrayfind9.js
+++ b/jstests/core/query/array/arrayfind9.js
@@ -1,6 +1,6 @@
 // Assorted $elemMatch behavior checks.
 
-t = db.jstests_arrayfind9;
+let t = db.jstests_arrayfind9;
 t.drop();
 
 // Top level field $elemMatch:$not matching
@@ -27,8 +27,8 @@ t.drop();
 t.save({a: [{b: [0, 2]}]});
 t.createIndex({a: 1});
 t.createIndex({'a.b': 1});
-plans = [{$natural: 1}, {a: 1}, {'a.b': 1}];
-for (i in plans) {
-    p = plans[i];
+let plans = [{$natural: 1}, {a: 1}, {'a.b': 1}];
+for (let i in plans) {
+    let p = plans[i];
     assert.eq(1, t.find({a: {$elemMatch: {b: {$gte: 1, $lte: 1}}}}).hint(p).itcount());
 }
diff --git a/jstests/core/query/array/arrayfinda.js b/jstests/core/query/array/arrayfinda.js
index 163af3d8d29..f79c7bf7a37 100644
--- a/jstests/core/query/array/arrayfinda.js
+++ b/jstests/core/query/array/arrayfinda.js
@@ -1,6 +1,6 @@
 // Assorted $elemMatch matching behavior checks.
 
-t = db.jstests_arrayfinda;
+let t = db.jstests_arrayfinda;
 t.drop();
 
 // $elemMatch only matches elements within arrays (a descriptive, not a normative test).
diff --git a/jstests/core/query/basic1.js b/jstests/core/query/basic1.js
index cc2917fb5a3..6ed22a1422c 100644
--- a/jstests/core/query/basic1.js
+++ b/jstests/core/query/basic1.js
@@ -1,11 +1,9 @@
 // @tags: [does_not_support_stepdowns]
 
-t = db.getCollection("basic1");
+let t = db.getCollection("basic1");
 t.drop();
 
-o = {
-    a: 1
-};
+let o = {a: 1};
 t.save(o);
 
 assert.eq(1, t.findOne().a, "first");
diff --git a/jstests/core/query/basic2.js b/jstests/core/query/basic2.js
index 3500d9fbdb5..d4501e3474f 100644
--- a/jstests/core/query/basic2.js
+++ b/jstests/core/query/basic2.js
@@ -3,12 +3,10 @@
 //   requires_non_retryable_writes,
 // ]
 
-t = db.getCollection("basic2");
+let t = db.getCollection("basic2");
 t.drop();
 
-o = {
-    n: 2
-};
+let o = {n: 2};
 t.save(o);
 
 assert.eq(1, t.find().count());
diff --git a/jstests/core/query/basic4.js b/jstests/core/query/basic4.js
index 4b2cf6f96be..e94c5868c80 100644
--- a/jstests/core/query/basic4.js
+++ b/jstests/core/query/basic4.js
@@ -1,4 +1,4 @@
-t = db.getCollection("basic4");
+let t = db.getCollection("basic4");
 t.drop();
 
 t.save({a: 1, b: 1.0});
diff --git a/jstests/core/query/basic5.js b/jstests/core/query/basic5.js
index 7ec41ef7872..e1a0df35bbb 100644
--- a/jstests/core/query/basic5.js
+++ b/jstests/core/query/basic5.js
@@ -1,4 +1,4 @@
-t = db.getCollection("basic5");
+let t = db.getCollection("basic5");
 t.drop();
 
 t.save({a: 1, b: [1, 2, 3]});
diff --git a/jstests/core/query/basic6.js b/jstests/core/query/basic6.js
index 89aef4acc2e..fb8d85b2f79 100644
--- a/jstests/core/query/basic6.js
+++ b/jstests/core/query/basic6.js
@@ -4,7 +4,7 @@
  * ]
  */
 
-t = db.basic6;
+let t = db.basic6;
 
 t.findOne();
 t.a.findOne();
diff --git a/jstests/core/query/basic7.js b/jstests/core/query/basic7.js
index dc6f18cc95b..33403380355 100644
--- a/jstests/core/query/basic7.js
+++ b/jstests/core/query/basic7.js
@@ -1,5 +1,5 @@
 
-t = db.basic7;
+let t = db.basic7;
 t.drop();
 
 t.save({a: 1});
diff --git a/jstests/core/query/basic8.js b/jstests/core/query/basic8.js
index 4a35de6963b..58ab069fa3b 100644
--- a/jstests/core/query/basic8.js
+++ b/jstests/core/query/basic8.js
@@ -1,10 +1,10 @@
 // @tags: [requires_fastcount]
 
-t = db.basic8;
+let t = db.basic8;
 t.drop();
 
 t.save({a: 1});
-o = t.findOne();
+let o = t.findOne();
 o.b = 2;
 t.save(o);
 
diff --git a/jstests/core/query/basica.js b/jstests/core/query/basica.js
index 1fe8b7c5de4..569b41ee90d 100644
--- a/jstests/core/query/basica.js
+++ b/jstests/core/query/basica.js
@@ -1,11 +1,11 @@
 
-t = db.basica;
+let t = db.basica;
 
 t.drop();
 
 t.save({a: 1, b: [{x: 2, y: 2}, {x: 3, y: 3}]});
 
-x = t.findOne();
+let x = t.findOne();
 x.b["0"].x = 4;
 x.b["0"].z = 4;
 x.b[0].m = 9;
diff --git a/jstests/core/query/count/count3.js b/jstests/core/query/count/count3.js
index d93df020f0b..51fb5d5d4c8 100644
--- a/jstests/core/query/count/count3.js
+++ b/jstests/core/query/count/count3.js
@@ -1,5 +1,5 @@
 
-t = db.count3;
+let t = db.count3;
 
 t.drop();
 
diff --git a/jstests/core/query/count/count5.js b/jstests/core/query/count/count5.js
index ceedf62b336..81fd8786bfc 100644
--- a/jstests/core/query/count/count5.js
+++ b/jstests/core/query/count/count5.js
@@ -1,15 +1,13 @@
 // @tags: [requires_fastcount]
 
-t = db.count5;
+let t = db.count5;
 t.drop();
 
-for (i = 0; i < 100; i++) {
+for (let i = 0; i < 100; i++) {
     t.save({x: i});
 }
 
-q = {
-    x: {$gt: 25, $lte: 75}
-};
+let q = {x: {$gt: 25, $lte: 75}};
 
 assert.eq(50, t.find(q).count(), "A");
 assert.eq(50, t.find(q).itcount(), "B");
diff --git a/jstests/core/query/count/count6.js b/jstests/core/query/count/count6.js
index 78735c89c26..8814b2b76a0 100644
--- a/jstests/core/query/count/count6.js
+++ b/jstests/core/query/count/count6.js
@@ -2,7 +2,7 @@
 //
 // @tags: [requires_fastcount]
 
-t = db.jstests_count6;
+let t = db.jstests_count6;
 
 function checkCountForObject(obj) {
     t.drop();
diff --git a/jstests/core/query/count/count7.js b/jstests/core/query/count/count7.js
index 443134474a8..cef47b46c2c 100644
--- a/jstests/core/query/count/count7.js
+++ b/jstests/core/query/count/count7.js
@@ -2,7 +2,7 @@
 
 // Check normal count matching and deduping.
 
-t = db.jstests_count7;
+let t = db.jstests_count7;
 t.drop();
 
 t.createIndex({a: 1});
diff --git a/jstests/core/query/count/count9.js b/jstests/core/query/count/count9.js
index 062f099e513..250ada94cb1 100644
--- a/jstests/core/query/count/count9.js
+++ b/jstests/core/query/count/count9.js
@@ -1,6 +1,6 @@
 // Test fast mode count with multikey entries.
 
-t = db.jstests_count9;
+let t = db.jstests_count9;
 t.drop();
 
 t.createIndex({a: 1});
diff --git a/jstests/core/query/count/countb.js b/jstests/core/query/count/countb.js
index 869825b25a1..cbce10c7e4e 100644
--- a/jstests/core/query/count/countb.js
+++ b/jstests/core/query/count/countb.js
@@ -4,7 +4,7 @@
 //     requires_scripting,
 // ]
 
-t = db.jstests_countb;
+let t = db.jstests_countb;
 t.drop();
 
 t.createIndex({a: 1});
diff --git a/jstests/core/query/cursor/cursor1.js b/jstests/core/query/cursor/cursor1.js
index 1cb00cc82fb..458787bf6d0 100644
--- a/jstests/core/query/cursor/cursor1.js
+++ b/jstests/core/query/cursor/cursor1.js
@@ -1,13 +1,13 @@
 // @tags: [requires_getmore, requires_fastcount]
 
-t = db.cursor1;
+let t = db.cursor1;
 t.drop();
 
-big = "";
+let big = "";
 while (big.length < 50000)
     big += "asdasdasdasdsdsdadsasdasdasD";
 
-num = Math.ceil(10000000 / big.length);
+let num = Math.ceil(10000000 / big.length);
 
 for (var i = 0; i < num; i++) {
     t.save({num: i, str: big});
diff --git a/jstests/core/query/cursor/cursor3.js b/jstests/core/query/cursor/cursor3.js
index 8e5672d4b3b..acf1339c345 100644
--- a/jstests/core/query/cursor/cursor3.js
+++ b/jstests/core/query/cursor/cursor3.js
@@ -4,19 +4,19 @@
 //   assumes_read_concern_local,
 // ]
 
-testNum = 1;
+let testNum = 1;
 
 function checkResults(expected, cursor, testNum) {
     assert.eq(expected.length,
               cursor.count(),
               "testNum: " + testNum + " A : " + tojson(cursor.toArray()) + " " +
                   tojson(cursor.explain()));
-    for (i = 0; i < expected.length; ++i) {
+    for (let i = 0; i < expected.length; ++i) {
         assert.eq(expected[i], cursor[i]["a"], "testNum: " + testNum + " B");
     }
 }
 
-t = db.cursor3;
+let t = db.cursor3;
 t.drop();
 
 t.save({a: 0});
diff --git a/jstests/core/query/cursor/cursor4.js b/jstests/core/query/cursor/cursor4.js
index d0440d329f1..32688ef7c55 100644
--- a/jstests/core/query/cursor/cursor4.js
+++ b/jstests/core/query/cursor/cursor4.js
@@ -2,21 +2,21 @@
 
 function checkResults(expected, cursor) {
     assert.eq(expected.length, cursor.count());
-    for (i = 0; i < expected.length; ++i) {
+    for (let i = 0; i < expected.length; ++i) {
         assert.eq(expected[i].a, cursor[i].a);
         assert.eq(expected[i].b, cursor[i].b);
     }
 }
 
 function testConstrainedFindMultiFieldSorting(db) {
-    r = db.ed_db_cursor4_cfmfs;
+    let r = db.ed_db_cursor4_cfmfs;
     r.drop();
 
-    entries = [{a: 0, b: 0}, {a: 0, b: 1}, {a: 1, b: 1}, {a: 1, b: 1}, {a: 2, b: 0}];
-    for (i = 0; i < entries.length; ++i)
+    let entries = [{a: 0, b: 0}, {a: 0, b: 1}, {a: 1, b: 1}, {a: 1, b: 1}, {a: 2, b: 0}];
+    for (let i = 0; i < entries.length; ++i)
         r.save(entries[i]);
     r.createIndex({a: 1, b: 1});
-    reverseEntries = entries.slice();
+    let reverseEntries = entries.slice();
     reverseEntries.reverse();
 
     checkResults(entries.slice(2, 4), r.find({a: 1, b: 1}).sort({a: 1, b: 1}).hint({a: 1, b: 1}));
diff --git a/jstests/core/query/cursor/cursor5.js b/jstests/core/query/cursor/cursor5.js
index aab03473255..e3764fdf039 100644
--- a/jstests/core/query/cursor/cursor5.js
+++ b/jstests/core/query/cursor/cursor5.js
@@ -2,7 +2,7 @@
 
 function checkResults(expected, cursor) {
     assert.eq(expected.length, cursor.count());
-    for (i = 0; i < expected.length; ++i) {
+    for (let i = 0; i < expected.length; ++i) {
         assert.eq(expected[i].a.b, cursor[i].a.b);
         assert.eq(expected[i].a.c, cursor[i].a.c);
         assert.eq(expected[i].a.d, cursor[i].a.d);
@@ -11,10 +11,10 @@ function checkResults(expected, cursor) {
 }
 
 function testBoundsWithSubobjectIndexes(db) {
-    r = db.ed_db_cursor5_bwsi;
+    let r = db.ed_db_cursor5_bwsi;
     r.drop();
 
-    z = [
+    let z = [
         {a: {b: 1, c: 2, d: 3}, e: 4},
         {a: {b: 1, c: 2, d: 3}, e: 5},
         {a: {b: 1, c: 2, d: 4}, e: 4},
@@ -22,10 +22,10 @@ function testBoundsWithSubobjectIndexes(db) {
         {a: {b: 2, c: 2, d: 3}, e: 4},
         {a: {b: 2, c: 2, d: 3}, e: 5}
     ];
-    for (i = 0; i < z.length; ++i)
+    for (let i = 0; i < z.length; ++i)
         r.save(z[i]);
-    idx = {"a.d": 1, a: 1, e: -1};
-    rIdx = {"a.d": -1, a: -1, e: 1};
+    let idx = {"a.d": 1, a: 1, e: -1};
+    let rIdx = {"a.d": -1, a: -1, e: 1};
     r.createIndex(idx);
 
     checkResults([z[0], z[4], z[2]], r.find({e: 4}).sort(idx).hint(idx));
diff --git a/jstests/core/query/cursor/cursor6.js b/jstests/core/query/cursor/cursor6.js
index dde1f9069cb..ad55dad6d25 100644
--- a/jstests/core/query/cursor/cursor6.js
+++ b/jstests/core/query/cursor/cursor6.js
@@ -13,7 +13,7 @@ function check(indexed) {
         hint = {$natural: 1};
     }
 
-    f = r.find().sort({a: 1, b: 1}).hint(hint);
+    let f = r.find().sort({a: 1, b: 1}).hint(hint);
     eq(z[0], f[0]);
     eq(z[1], f[1]);
     eq(z[2], f[2]);
@@ -50,11 +50,11 @@ function check(indexed) {
     eq(z[0], f[3]);
 }
 
-r = db.ed_db_cursor6;
+let r = db.ed_db_cursor6;
 r.drop();
 
-z = [{a: 1, b: 1}, {a: 1, b: 2}, {a: 2, b: 1}, {a: 2, b: 2}];
-for (i = 0; i < z.length; ++i)
+let z = [{a: 1, b: 1}, {a: 1, b: 2}, {a: 2, b: 1}, {a: 2, b: 2}];
+for (let i = 0; i < z.length; ++i)
     r.save(z[i]);
 
 r.createIndex({a: 1, b: -1});
diff --git a/jstests/core/query/cursor/cursor7.js b/jstests/core/query/cursor/cursor7.js
index 4a21c420274..9e75ff605ff 100644
--- a/jstests/core/query/cursor/cursor7.js
+++ b/jstests/core/query/cursor/cursor7.js
@@ -2,21 +2,21 @@
 
 function checkResults(expected, cursor) {
     assert.eq(expected.length, cursor.count());
-    for (i = 0; i < expected.length; ++i) {
+    for (let i = 0; i < expected.length; ++i) {
         assert.eq(expected[i].a, cursor[i].a);
         assert.eq(expected[i].b, cursor[i].b);
     }
 }
 
 function testMultipleInequalities(db) {
-    r = db.ed_db_cursor_mi;
+    let r = db.ed_db_cursor_mi;
     r.drop();
 
-    z = [{a: 1, b: 2}, {a: 3, b: 4}, {a: 5, b: 6}, {a: 7, b: 8}];
-    for (i = 0; i < z.length; ++i)
+    let z = [{a: 1, b: 2}, {a: 3, b: 4}, {a: 5, b: 6}, {a: 7, b: 8}];
+    for (let i = 0; i < z.length; ++i)
         r.save(z[i]);
-    idx = {a: 1, b: 1};
-    rIdx = {a: -1, b: -1};
+    let idx = {a: 1, b: 1};
+    let rIdx = {a: -1, b: -1};
     r.createIndex(idx);
 
     checkResults([z[2], z[3]], r.find({a: {$gt: 3}}).sort(idx).hint(idx));
diff --git a/jstests/core/query/cursor/tailable_cursor_invalidation.js b/jstests/core/query/cursor/tailable_cursor_invalidation.js
index d59e852d63d..1cd82554ef5 100644
--- a/jstests/core/query/cursor/tailable_cursor_invalidation.js
+++ b/jstests/core/query/cursor/tailable_cursor_invalidation.js
@@ -6,6 +6,7 @@
 //   # This test has statements that do not support non-local read concern.
 //   does_not_support_causal_consistency,
 // ]
+load("jstests/libs/fixture_helpers.js");
 
 // Tests for the behavior of tailable cursors when a collection is dropped or the cursor is
 // otherwise invalidated.
@@ -26,8 +27,7 @@ const emptyBatchCursorId = assert
                                .commandWorked(db.runCommand(
                                    {find: collName, tailable: true, awaitData: true, batchSize: 0}))
                                .cursor.id;
-const isMongos = db.adminCommand({isdbgrid: 1}).isdbgrid;
-if (isMongos) {
+if (FixtureHelpers.isMongos(db)) {
     // Mongos will let you establish a cursor with batch size 0 and return to you before it
     // realizes the shard's cursor is exhausted. The next getMore should return a 0 cursor id
     // though.
diff --git a/jstests/core/query/date/date1.js b/jstests/core/query/date/date1.js
index 65449c662b5..f5e608bbaeb 100644
--- a/jstests/core/query/date/date1.js
+++ b/jstests/core/query/date/date1.js
@@ -1,5 +1,5 @@
 
-t = db.date1;
+let t = db.date1;
 
 function go(d, msg) {
     t.drop();
diff --git a/jstests/core/query/date/date2.js b/jstests/core/query/date/date2.js
index a398058d771..b1d8c3d8b2f 100644
--- a/jstests/core/query/date/date2.js
+++ b/jstests/core/query/date/date2.js
@@ -1,6 +1,6 @@
 // Check that it's possible to compare a Date to a Timestamp, but they are never equal - SERVER-3304
 
-t = db.jstests_date2;
+let t = db.jstests_date2;
 t.drop();
 
 t.createIndex({a: 1});
diff --git a/jstests/core/query/date/date3.js b/jstests/core/query/date/date3.js
index e3eaea620ec..06f8af3fce7 100644
--- a/jstests/core/query/date/date3.js
+++ b/jstests/core/query/date/date3.js
@@ -2,12 +2,12 @@
 //
 // @tags: [requires_fastcount]
 
-t = db.date3;
+let t = db.date3;
 t.drop();
 
-d1 = new Date(-1000);
-dz = new Date(0);
-d2 = new Date(1000);
+let d1 = new Date(-1000);
+let dz = new Date(0);
+let d2 = new Date(1000);
 
 t.save({x: 3, d: dz});
 t.save({x: 2, d: d2});
diff --git a/jstests/core/query/dbref/dbref1.js b/jstests/core/query/dbref/dbref1.js
index b5bb06f230d..da88f8d5525 100644
--- a/jstests/core/query/dbref/dbref1.js
+++ b/jstests/core/query/dbref/dbref1.js
@@ -1,6 +1,6 @@
 
-a = db.dbref1a;
-b = db.dbref1b;
+let a = db.dbref1a;
+let b = db.dbref1b;
 
 a.drop();
 b.drop();
diff --git a/jstests/core/query/dbref/dbref2.js b/jstests/core/query/dbref/dbref2.js
index be0deefeb2d..4efddccbbac 100644
--- a/jstests/core/query/dbref/dbref2.js
+++ b/jstests/core/query/dbref/dbref2.js
@@ -1,6 +1,6 @@
-a = db.dbref2a;
-b = db.dbref2b;
-c = db.dbref2c;
+let a = db.dbref2a;
+let b = db.dbref2b;
+let c = db.dbref2c;
 
 a.drop();
 b.drop();
diff --git a/jstests/core/query/dbref/ref.js b/jstests/core/query/dbref/ref.js
index 0d1160482fc..696b44c7d91 100644
--- a/jstests/core/query/dbref/ref.js
+++ b/jstests/core/query/dbref/ref.js
@@ -10,7 +10,7 @@ assert.throws(function() {
 });
 
 db.things.save({name: "abc"});
-x = db.things.findOne();
+let x = db.things.findOne();
 x.o = new DBPointer("otherthings", other._id);
 db.things.save(x);
 
diff --git a/jstests/core/query/dbref/ref2.js b/jstests/core/query/dbref/ref2.js
index 6b284b1f59f..a17b084e8b1 100644
--- a/jstests/core/query/dbref/ref2.js
+++ b/jstests/core/query/dbref/ref2.js
@@ -1,16 +1,10 @@
 // @tags: [requires_fastcount]
 
-t = db.ref2;
+let t = db.ref2;
 t.drop();
 
-a = {
-    $ref: "foo",
-    $id: 1
-};
-b = {
-    $ref: "foo",
-    $id: 2
-};
+let a = {$ref: "foo", $id: 1};
+let b = {$ref: "foo", $id: 2};
 
 t.save({name: "a", r: a});
 t.save({name: "b", r: b});
diff --git a/jstests/core/query/dbref/ref3.js b/jstests/core/query/dbref/ref3.js
index 4406863d899..f73c7d0fad4 100644
--- a/jstests/core/query/dbref/ref3.js
+++ b/jstests/core/query/dbref/ref3.js
@@ -8,7 +8,7 @@ var other = {s: "other thing", n: 1};
 db.otherthings3.save(other);
 
 db.things3.save({name: "abc"});
-x = db.things3.findOne();
+let x = db.things3.findOne();
 x.o = new DBRef("otherthings3", other._id);
 db.things3.save(x);
 
diff --git a/jstests/core/query/dbref/ref4.js b/jstests/core/query/dbref/ref4.js
index 882253f3883..45519b8cac1 100644
--- a/jstests/core/query/dbref/ref4.js
+++ b/jstests/core/query/dbref/ref4.js
@@ -1,6 +1,6 @@
 
-a = db.ref4a;
-b = db.ref4b;
+let a = db.ref4a;
+let b = db.ref4b;
 
 a.drop();
 b.drop();
@@ -11,7 +11,7 @@ b.save(other);
 a.save({name: "abc", others: [new DBRef("ref4b", other._id), new DBPointer("ref4b", other._id)]});
 assert(a.findOne().others[0].fetch().n == 17, "dbref broken 1");
 
-x = Array.fetchRefs(a.findOne().others);
+let x = Array.fetchRefs(a.findOne().others);
 assert.eq(2, x.length, "A");
 assert.eq(17, x[0].n, "B");
 assert.eq(17, x[1].n, "C");
diff --git a/jstests/core/query/distinct/distinct2.js b/jstests/core/query/distinct/distinct2.js
index fc6ff7779b7..9b886e56b43 100644
--- a/jstests/core/query/distinct/distinct2.js
+++ b/jstests/core/query/distinct/distinct2.js
@@ -1,5 +1,5 @@
 
-t = db.distinct2;
+let t = db.distinct2;
 t.drop();
 
 t.save({a: null});
diff --git a/jstests/core/query/distinct/distinct3.js b/jstests/core/query/distinct/distinct3.js
index c2aaaad79e5..eb3a0077d9c 100644
--- a/jstests/core/query/distinct/distinct3.js
+++ b/jstests/core/query/distinct/distinct3.js
@@ -6,35 +6,35 @@
 
 // Yield and delete test case for query optimizer cursor.  SERVER-4401
 
-t = db.jstests_distinct3;
+let t = db.jstests_distinct3;
 t.drop();
 
 t.createIndex({a: 1});
 t.createIndex({b: 1});
 
 var bulk = t.initializeUnorderedBulkOp();
-for (i = 0; i < 50; ++i) {
-    for (j = 0; j < 2; ++j) {
+for (let i = 0; i < 50; ++i) {
+    for (let j = 0; j < 2; ++j) {
         bulk.insert({a: i, c: i, d: j});
     }
 }
-for (i = 0; i < 100; ++i) {
+for (let i = 0; i < 100; ++i) {
     bulk.insert({b: i, c: i + 50});
 }
 assert.commandWorked(bulk.execute());
 
 // Attempt to remove the last match for the {a:1} index scan while distinct is yielding.
-p = startParallelShell('for( i = 0; i < 100; ++i ) {                              ' +
-                       '    var bulk = db.jstests_distinct3.initializeUnorderedBulkOp();' +
-                       '    bulk.find( { a:49 } ).remove();                       ' +
-                       '    for( j = 0; j < 20; ++j ) {                           ' +
-                       '        bulk.insert( { a:49, c:49, d:j } );               ' +
-                       '    }                                                     ' +
-                       '    assert.commandWorked(bulk.execute());                       ' +
-                       '}                                                         ');
+let p = startParallelShell('for( i = 0; i < 100; ++i ) {                              ' +
+                           '    var bulk = db.jstests_distinct3.initializeUnorderedBulkOp();' +
+                           '    bulk.find( { a:49 } ).remove();                       ' +
+                           '    for( j = 0; j < 20; ++j ) {                           ' +
+                           '        bulk.insert( { a:49, c:49, d:j } );               ' +
+                           '    }                                                     ' +
+                           '    assert.commandWorked(bulk.execute());                       ' +
+                           '}                                                         ');
 
-for (i = 0; i < 100; ++i) {
-    count = t.distinct('c', {$or: [{a: {$gte: 0}, d: 0}, {b: {$gte: 0}}]}).length;
+for (let i = 0; i < 100; ++i) {
+    let count = t.distinct('c', {$or: [{a: {$gte: 0}, d: 0}, {b: {$gte: 0}}]}).length;
     assert.gt(count, 100);
 }
 
diff --git a/jstests/core/query/distinct/distinct_array1.js b/jstests/core/query/distinct/distinct_array1.js
index cb82c25bbff..a812c1c23f0 100644
--- a/jstests/core/query/distinct/distinct_array1.js
+++ b/jstests/core/query/distinct/distinct_array1.js
@@ -1,4 +1,4 @@
-t = db.distinct_array1;
+let t = db.distinct_array1;
 t.drop();
 
 t.save({a: [1, 2, 3]});
@@ -7,7 +7,7 @@ t.save({a: [3, 4, 5]});
 t.save({a: 9});
 
 // Without index.
-res = t.distinct("a").sort();
+let res = t.distinct("a").sort();
 assert.eq("1,2,3,4,5,9", res.toString());
 
 // Array element 0 without index.
diff --git a/jstests/core/query/exists/exists.js b/jstests/core/query/exists/exists.js
index b85d80c36a7..f29320b002e 100644
--- a/jstests/core/query/exists/exists.js
+++ b/jstests/core/query/exists/exists.js
@@ -2,7 +2,7 @@
 //   requires_fastcount,
 // ]
 
-t = db.jstests_exists;
+let t = db.jstests_exists;
 t.drop();
 
 t.save({});
diff --git a/jstests/core/query/exists/exists2.js b/jstests/core/query/exists/exists2.js
index 0764d859c3b..6d175584eec 100644
--- a/jstests/core/query/exists/exists2.js
+++ b/jstests/core/query/exists/exists2.js
@@ -1,4 +1,4 @@
-t = db.exists2;
+let t = db.exists2;
 t.drop();
 
 t.save({a: 1, b: 1});
diff --git a/jstests/core/query/exists/exists3.js b/jstests/core/query/exists/exists3.js
index 510d63c3752..1b5939f07ce 100644
--- a/jstests/core/query/exists/exists3.js
+++ b/jstests/core/query/exists/exists3.js
@@ -1,6 +1,6 @@
 // Check exists with non empty document, based on SERVER-2470 example.
 
-t = db.jstests_exists3;
+let t = db.jstests_exists3;
 t.drop();
 
 t.insert({a: 1, b: 2});
diff --git a/jstests/core/query/exists/exists4.js b/jstests/core/query/exists/exists4.js
index a533ca53e9c..4960fe32ff7 100644
--- a/jstests/core/query/exists/exists4.js
+++ b/jstests/core/query/exists/exists4.js
@@ -1,6 +1,6 @@
 // Check various exists cases, based on SERVER-1735 example.
 
-t = db.jstests_exists4;
+let t = db.jstests_exists4;
 t.drop();
 
 t.createIndex({date: -1, country_code: 1, user_id: 1}, {unique: 1, background: 1});
diff --git a/jstests/core/query/exists/exists5.js b/jstests/core/query/exists/exists5.js
index 2f4b1a9b8de..112e8243b99 100644
--- a/jstests/core/query/exists/exists5.js
+++ b/jstests/core/query/exists/exists5.js
@@ -1,6 +1,6 @@
 // Test some $not/$exists cases.
 
-t = db.jstests_exists5;
+let t = db.jstests_exists5;
 t.drop();
 
 t.save({a: 1});
diff --git a/jstests/core/query/exists/exists6.js b/jstests/core/query/exists/exists6.js
index 736574db895..71fd20d3c26 100644
--- a/jstests/core/query/exists/exists6.js
+++ b/jstests/core/query/exists/exists6.js
@@ -1,6 +1,6 @@
 // SERVER-393 Test indexed matching with $exists.
 
-t = db.jstests_exists6;
+let t = db.jstests_exists6;
 t.drop();
 
 t.createIndex({b: 1});
diff --git a/jstests/core/query/exists/exists7.js b/jstests/core/query/exists/exists7.js
index 285559e82f8..1f25db5fedf 100644
--- a/jstests/core/query/exists/exists7.js
+++ b/jstests/core/query/exists/exists7.js
@@ -2,7 +2,7 @@
 
 // Test that non boolean value types are allowed with $exists spec. SERVER-2322
 
-t = db.jstests_exists7;
+let t = db.jstests_exists7;
 t.drop();
 
 function testIntegerExistsSpec() {
diff --git a/jstests/core/query/exists/exists8.js b/jstests/core/query/exists/exists8.js
index f22a3be44f4..3c506cd5781 100644
--- a/jstests/core/query/exists/exists8.js
+++ b/jstests/core/query/exists/exists8.js
@@ -2,7 +2,7 @@
 
 // Test $exists with array element field names SERVER-2897
 
-t = db.jstests_exists8;
+let t = db.jstests_exists8;
 t.drop();
 
 t.save({a: [1]});
diff --git a/jstests/core/query/exists/exists9.js b/jstests/core/query/exists/exists9.js
index c187bb3a101..d822ae95f0a 100644
--- a/jstests/core/query/exists/exists9.js
+++ b/jstests/core/query/exists/exists9.js
@@ -1,6 +1,6 @@
 // SERVER-393 Test exists with various empty array and empty object cases.
 
-t = db.jstests_exists9;
+let t = db.jstests_exists9;
 t.drop();
 
 // Check existence of missing nested field.
diff --git a/jstests/core/query/exists/existsb.js b/jstests/core/query/exists/existsb.js
index 64ee3cf9a88..b327311a4ef 100644
--- a/jstests/core/query/exists/existsb.js
+++ b/jstests/core/query/exists/existsb.js
@@ -20,7 +20,7 @@
 //   everything but {} will have an index entry.
 // Let's make sure we handle this properly!
 
-t = db.jstests_existsb;
+let t = db.jstests_existsb;
 t.drop();
 
 t.save({});
diff --git a/jstests/core/query/explain/explain1.js b/jstests/core/query/explain/explain1.js
index 2de3e2f89d2..cdbd8751dda 100644
--- a/jstests/core/query/explain/explain1.js
+++ b/jstests/core/query/explain/explain1.js
@@ -2,16 +2,14 @@
 //   assumes_read_concern_local,
 // ]
 
-t = db.explain1;
+let t = db.explain1;
 t.drop();
 
 for (var i = 0; i < 100; i++) {
     t.save({x: i});
 }
 
-q = {
-    x: {$gt: 50}
-};
+let q = {x: {$gt: 50}};
 
 assert.eq(49, t.find(q).count(), "A");
 assert.eq(49, t.find(q).itcount(), "B");
diff --git a/jstests/core/query/explain/explain4.js b/jstests/core/query/explain/explain4.js
index e49b188cb65..f3e2b460c5e 100644
--- a/jstests/core/query/explain/explain4.js
+++ b/jstests/core/query/explain/explain4.js
@@ -3,16 +3,16 @@
 //   assumes_read_concern_local,
 // ]
 
-t = db.jstests_explain4;
+let t = db.jstests_explain4;
 t.drop();
 
 t.createIndex({a: 1});
 
-for (i = 0; i < 10; ++i) {
+for (let i = 0; i < 10; ++i) {
     t.save({a: i, b: 0});
 }
 
-explain = t.find({a: {$gte: 0}, b: 0}).sort({a: 1}).hint({a: 1}).limit(5).explain(true);
+let explain = t.find({a: {$gte: 0}, b: 0}).sort({a: 1}).hint({a: 1}).limit(5).explain(true);
 
 // Five results are expected, matching the limit spec.
 assert.eq(5, explain.executionStats.nReturned);
diff --git a/jstests/core/query/explain/explain6.js b/jstests/core/query/explain/explain6.js
index fbb6ecf6d76..73bfced5116 100644
--- a/jstests/core/query/explain/explain6.js
+++ b/jstests/core/query/explain/explain6.js
@@ -6,7 +6,7 @@
 // Basic test which checks the number of documents returned, keys examined, and documents
 // examined as reported by explain.
 
-t = db.jstests_explain6;
+let t = db.jstests_explain6;
 t.drop();
 
 t.createIndex({a: 1, b: 1});
@@ -15,7 +15,7 @@ t.createIndex({b: 1, a: 1});
 t.save({a: 0, b: 1});
 t.save({a: 1, b: 0});
 
-explain = t.find({a: {$gte: 0}, b: {$gte: 0}}).explain(true);
+let explain = t.find({a: {$gte: 0}, b: {$gte: 0}}).explain(true);
 
 assert.eq(2, explain.executionStats.nReturned);
 assert.eq(2, explain.executionStats.totalKeysExamined);
diff --git a/jstests/core/query/explain/explain_batch_size.js b/jstests/core/query/explain/explain_batch_size.js
index d31b54b3f16..aec1124f171 100644
--- a/jstests/core/query/explain/explain_batch_size.js
+++ b/jstests/core/query/explain/explain_batch_size.js
@@ -8,11 +8,11 @@
 //   requires_fastcount,
 // ]
 
-t = db.explain_batch_size;
+let t = db.explain_batch_size;
 t.drop();
 
 var n = 3;
-for (i = 0; i < n; i++) {
+for (let i = 0; i < n; i++) {
     t.save({x: i});
 }
 
diff --git a/jstests/core/query/expr/expr.js b/jstests/core/query/expr/expr.js
index 737cab39f15..81ebf13a8d3 100644
--- a/jstests/core/query/expr/expr.js
+++ b/jstests/core/query/expr/expr.js
@@ -15,13 +15,10 @@
 "use strict";
 
 load("jstests/libs/sbe_assert_error_override.js");  // For 'assert.errorCodeEq'.
+load("jstests/libs/fixture_helpers.js");
 
 const coll = db.expr;
 
-const hello = db.runCommand("hello");
-assert.commandWorked(hello);
-const isMongos = (hello.msg === "isdbgrid");
-
 //
 // $expr in aggregate.
 //
@@ -126,7 +123,7 @@ assert.throws(function() {
 // 'executionSuccess' field.
 let explain = coll.find({$expr: {$divide: [1, "$a"]}}).explain("executionStats");
 // Accommodate format differences between explain via mongos and explain directly on a mongod.
-if (!isMongos) {
+if (!FixtureHelpers.isMongos(db)) {
     assert(explain.hasOwnProperty("executionStats"), explain);
     assert.eq(explain.executionStats.executionSuccess, false, explain);
     assert.errorCodeEq(explain.executionStats.errorCode, [16609, ErrorCodes.TypeMismatch], explain);
diff --git a/jstests/core/query/find/find2.js b/jstests/core/query/find/find2.js
index a793c60b804..747775bd4b0 100644
--- a/jstests/core/query/find/find2.js
+++ b/jstests/core/query/find/find2.js
@@ -3,13 +3,13 @@
 // @tags: [requires_fastcount]
 
 function testObjectIdFind(db) {
-    r = db.ed_db_find2_oif;
+    let r = db.ed_db_find2_oif;
     r.drop();
 
-    for (i = 0; i < 3; ++i)
+    for (let i = 0; i < 3; ++i)
         r.save({});
 
-    f = r.find().sort({_id: 1});
+    let f = r.find().sort({_id: 1});
     assert.eq(3, f.count());
     assert(f[0]._id < f[1]._id);
     assert(f[1]._id < f[2]._id);
diff --git a/jstests/core/query/find/find6.js b/jstests/core/query/find/find6.js
index d76cc1d5fb5..4b90cfe8cf7 100644
--- a/jstests/core/query/find/find6.js
+++ b/jstests/core/query/find/find6.js
@@ -4,7 +4,7 @@
 //   requires_scripting,
 // ]
 
-t = db.find6;
+let t = db.find6;
 t.drop();
 
 t.save({a: 1});
@@ -16,7 +16,7 @@ assert.eq(1, t.find("function() { return this.b == null; }").itcount(), "C");
 assert.eq(1, t.find("function() { return this.b == null; }").count(), "D");
 
 /* test some stuff with dot array notation */
-q = db.find6a;
+let q = db.find6a;
 q.drop();
 q.insert({"a": [{"0": 1}]});
 q.insert({"a": [{"0": 2}]});
diff --git a/jstests/core/query/find/find7.js b/jstests/core/query/find/find7.js
index ed18dcbb0ff..56fbd859299 100644
--- a/jstests/core/query/find/find7.js
+++ b/jstests/core/query/find/find7.js
@@ -1,10 +1,7 @@
-t = db.find7;
+let t = db.find7;
 t.drop();
 
-x = {
-    "_id": {"d": 3649, "w": "signed"},
-    "u": {"3649": 5}
-};
+let x = {"_id": {"d": 3649, "w": "signed"}, "u": {"3649": 5}};
 t.insert(x);
 assert.eq(x, t.findOne(), "A1");
 assert.eq(x, t.findOne({_id: x._id}), "A2");
diff --git a/jstests/core/query/find/find8.js b/jstests/core/query/find/find8.js
index 14930a056e7..a64f89496f5 100644
--- a/jstests/core/query/find/find8.js
+++ b/jstests/core/query/find/find8.js
@@ -1,6 +1,6 @@
 // SERVER-1932 Test unindexed matching of a range that is only valid in a multikey context.
 
-t = db.jstests_find8;
+let t = db.jstests_find8;
 t.drop();
 
 t.save({a: [1, 10]});
diff --git a/jstests/core/query/find/find9.js b/jstests/core/query/find/find9.js
index be6bfdb2ccf..e4858e09490 100644
--- a/jstests/core/query/find/find9.js
+++ b/jstests/core/query/find/find9.js
@@ -2,11 +2,11 @@
 
 // Test that the MaxBytesToReturnToClientAtOnce limit is enforced.
 
-t = db.jstests_find9;
+let t = db.jstests_find9;
 t.drop();
 
-big = new Array(500000).toString();
-for (i = 0; i < 60; ++i) {
+let big = new Array(500000).toString();
+for (let i = 0; i < 60; ++i) {
     t.save({a: i, b: big});
 }
 
@@ -18,12 +18,12 @@ assert.gt(60, t.find().objsLeftInBatch());
 assert.eq(60, t.find({}, {a: 1}).batchSize(80).objsLeftInBatch());
 assert.gt(60, t.find().batchSize(80).objsLeftInBatch());
 
-for (i = 0; i < 60; ++i) {
+for (let i = 0; i < 60; ++i) {
     t.save({a: i, b: big});
 }
 
 // Check size limit with get more.
-c = t.find().batchSize(80);
+let c = t.find().batchSize(80);
 while (c.hasNext()) {
     assert.gt(60, c.objsLeftInBatch());
     c.next();
diff --git a/jstests/core/query/find/finda.js b/jstests/core/query/find/finda.js
index 2e1a93cbad8..2a3799f72bf 100644
--- a/jstests/core/query/find/finda.js
+++ b/jstests/core/query/find/finda.js
@@ -4,10 +4,10 @@
 
 // Tests where the QueryOptimizerCursor enters takeover mode during a query rather than a get more.
 
-t = db.jstests_finda;
+let t = db.jstests_finda;
 t.drop();
 
-numDocs = 200;
+let numDocs = 200;
 
 function clearQueryPlanCache() {
     t.createIndex({c: 1});
@@ -16,12 +16,12 @@ function clearQueryPlanCache() {
 
 function assertAllFound(matches) {
     //    printjson( matches );
-    found = new Array(numDocs);
+    let found = new Array(numDocs);
     for (var i = 0; i < numDocs; ++i) {
         found[i] = false;
     }
     for (var i in matches) {
-        m = matches[i];
+        let m = matches[i];
         found[m._id] = true;
     }
     for (var i = 0; i < numDocs; ++i) {
@@ -34,7 +34,7 @@ function makeCursor(query, projection, sort, batchSize, returnKey) {
     printjson(query);
     print("proj:");
     printjson(projection);
-    cursor = t.find(query, projection);
+    let cursor = t.find(query, projection);
     if (sort) {
         cursor.sort(sort);
         print("sort:");
@@ -53,7 +53,7 @@ function makeCursor(query, projection, sort, batchSize, returnKey) {
 function checkCursorWithBatchSizeProjection(
     query, projection, sort, batchSize, expectedLeftInBatch) {
     clearQueryPlanCache();
-    cursor = makeCursor(query, projection, sort, batchSize);
+    let cursor = makeCursor(query, projection, sort, batchSize);
     if (TestData.batchSize && batchSize == null) {
         expectedLeftInBatch = Math.min(TestData.batchSize, expectedLeftInBatch);
     }
@@ -71,10 +71,10 @@ function checkCursorWithBatchSize(query, sort, batchSize, expectedLeftInBatch) {
     // from the a,_id index.
     clearQueryPlanCache();
     if (expectedLeftInBatch > 110) {
-        cursor = makeCursor(query, {}, sort, batchSize, true);
-        lastNonAIndexResult = -1;
+        let cursor = makeCursor(query, {}, sort, batchSize, true);
+        let lastNonAIndexResult = -1;
         for (var i = 0; i < expectedLeftInBatch; ++i) {
-            next = cursor.next();
+            let next = cursor.next();
             // Identify the query plan used by checking the fields of a returnKey query.
             if (!friendlyEqual(['a', '_id'], Object.keySet(next))) {
                 lastNonAIndexResult = i;
diff --git a/jstests/core/query/in/in.js b/jstests/core/query/in/in.js
index ca8cd77b189..f2a3ab6fcff 100644
--- a/jstests/core/query/in/in.js
+++ b/jstests/core/query/in/in.js
@@ -1,5 +1,5 @@
 
-t = db.in1;
+let t = db.in1;
 t.drop();
 
 t.save({a: 1});
diff --git a/jstests/core/query/in/in2.js b/jstests/core/query/in/in2.js
index 6682bbc79c1..48f94f6aed6 100644
--- a/jstests/core/query/in/in2.js
+++ b/jstests/core/query/in/in2.js
@@ -1,5 +1,5 @@
 
-t = db.in2;
+let t = db.in2;
 
 function go(name, index) {
     t.drop();
diff --git a/jstests/core/query/in/in3.js b/jstests/core/query/in/in3.js
index bd64329ded4..5bc2b353b45 100644
--- a/jstests/core/query/in/in3.js
+++ b/jstests/core/query/in/in3.js
@@ -1,6 +1,6 @@
 // SERVER-2829 Test arrays matching themselves within a $in expression.
 
-t = db.jstests_in8;
+let t = db.jstests_in8;
 t.drop();
 
 t.save({key: [1]});
diff --git a/jstests/core/query/in/in4.js b/jstests/core/query/in/in4.js
index e916ca7c82d..8d18a8b4287 100644
--- a/jstests/core/query/in/in4.js
+++ b/jstests/core/query/in/in4.js
@@ -2,7 +2,7 @@
 
 // SERVER-2343 Test $in empty array matching.
 
-t = db.jstests_in9;
+let t = db.jstests_in9;
 t.drop();
 
 function someData() {
diff --git a/jstests/core/query/in/in5.js b/jstests/core/query/in/in5.js
index 80f37e6b473..5a8e63d1888 100644
--- a/jstests/core/query/in/in5.js
+++ b/jstests/core/query/in/in5.js
@@ -4,28 +4,28 @@
 //   assumes_no_implicit_index_creation,
 // ]
 
-t = db.in5;
+let t = db.in5;
 
 function go(fn) {
     t.drop();
-    o = {};
+    let o = {};
     o[fn] = {a: 1, b: 2};
     t.insert(o);
 
-    x = {};
+    let x = {};
     x[fn] = {a: 1, b: 2};
     assert.eq(1, t.find(x).itcount(), "A1 - " + fn);
 
-    y = {};
+    let y = {};
     y[fn] = {$in: [{a: 1, b: 2}]};
     assert.eq(1, t.find(y).itcount(), "A2 - " + fn);
 
-    z = {};
+    let z = {};
     z[fn + ".a"] = 1;
     z[fn + ".b"] = {$in: [2]};
     assert.eq(1, t.find(z).itcount(), "A3 - " + fn);  // SERVER-1366
 
-    i = {};
+    let i = {};
     i[fn] = 1;
     t.createIndex(i);
 
diff --git a/jstests/core/query/in/in6.js b/jstests/core/query/in/in6.js
index ab8322cfe0a..8584e1ee954 100644
--- a/jstests/core/query/in/in6.js
+++ b/jstests/core/query/in/in6.js
@@ -1,4 +1,4 @@
-t = db.jstests_in6;
+let t = db.jstests_in6;
 t.drop();
 
 t.save({});
diff --git a/jstests/core/query/in/in7.js b/jstests/core/query/in/in7.js
index 78caf6a85f1..ee2de08c0f4 100644
--- a/jstests/core/query/in/in7.js
+++ b/jstests/core/query/in/in7.js
@@ -1,6 +1,6 @@
 // Uassert when $elemMatch is attempted within $in SERVER-3545
 
-t = db.jstests_ina;
+let t = db.jstests_ina;
 t.drop();
 t.save({});
 
diff --git a/jstests/core/query/in/in8.js b/jstests/core/query/in/in8.js
index f1b6188347c..42a99407ce0 100644
--- a/jstests/core/query/in/in8.js
+++ b/jstests/core/query/in/in8.js
@@ -1,6 +1,6 @@
 // Test $in regular expressions with overlapping index bounds.  SERVER-4677
 
-t = db.jstests_inb;
+let t = db.jstests_inb;
 t.drop();
 
 function checkResults(query) {
diff --git a/jstests/core/query/inc/inc1.js b/jstests/core/query/inc/inc1.js
index 551d15e0f63..2470b146d70 100644
--- a/jstests/core/query/inc/inc1.js
+++ b/jstests/core/query/inc/inc1.js
@@ -1,6 +1,6 @@
 // @tags: [requires_fastcount]
 
-t = db.inc1;
+let t = db.inc1;
 t.drop();
 
 function test(num, name) {
diff --git a/jstests/core/query/inc/inc2.js b/jstests/core/query/inc/inc2.js
index debdfde82cb..1d253723b28 100644
--- a/jstests/core/query/inc/inc2.js
+++ b/jstests/core/query/inc/inc2.js
@@ -1,5 +1,5 @@
 
-t = db.inc2;
+let t = db.inc2;
 t.drop();
 
 t.save({_id: 1, x: 1});
diff --git a/jstests/core/query/inc/inc3.js b/jstests/core/query/inc/inc3.js
index e24165876c6..51a9c9c1587 100644
--- a/jstests/core/query/inc/inc3.js
+++ b/jstests/core/query/inc/inc3.js
@@ -3,7 +3,7 @@
 // key.
 // @tags: [assumes_unsharded_collection]
 
-t = db.inc3;
+let t = db.inc3;
 
 t.drop();
 t.save({_id: 1, z: 1, a: 1});
diff --git a/jstests/core/query/js/js1.js b/jstests/core/query/js/js1.js
index f569606ba54..0a9254c0154 100644
--- a/jstests/core/query/js/js1.js
+++ b/jstests/core/query/js/js1.js
@@ -4,7 +4,7 @@
 //   requires_scripting,
 // ]
 
-t = db.jstests_js1;
+let t = db.jstests_js1;
 t.remove({});
 
 t.save({z: 1});
diff --git a/jstests/core/query/js/js2.js b/jstests/core/query/js/js2.js
index a278a520a88..05daee83940 100644
--- a/jstests/core/query/js/js2.js
+++ b/jstests/core/query/js/js2.js
@@ -2,10 +2,10 @@
 //   requires_non_retryable_writes
 //]
 
-t = db.jstests_js2;
+let t = db.jstests_js2;
 t.remove({});
 
-t2 = db.jstests_js2_2;
+let t2 = db.jstests_js2_2;
 t2.remove({});
 
 assert.eq(0, t2.find().length(), "A");
diff --git a/jstests/core/query/js/js3.js b/jstests/core/query/js/js3.js
index c9239bb4176..cb2b03e7787 100644
--- a/jstests/core/query/js/js3.js
+++ b/jstests/core/query/js/js3.js
@@ -7,13 +7,13 @@
 //   requires_scripting,
 // ]
 
-t = db.jstests_js3;
+let t = db.jstests_js3;
 
-debug = function(s) {
+let debug = function(s) {
     // printjson( s );
 };
 
-for (z = 0; z < 2; z++) {
+for (let z = 0; z < 2; z++) {
     debug(z);
 
     t.drop();
@@ -23,7 +23,7 @@ for (z = 0; z < 2; z++) {
         t.createIndex({i: 1});
     }
 
-    for (i = 0; i < 1000; i++)
+    for (let i = 0; i < 1000; i++)
         t.save({
             i: i,
             z: "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
@@ -57,17 +57,17 @@ for (z = 0; z < 2; z++) {
 
     debug("before indexed find");
 
-    arr = t.find({
-               $where: function() {
-                   return obj.i == 7 || obj.i == 8;
-               }
-           }).toArray();
+    let arr = t.find({
+                   $where: function() {
+                       return obj.i == 7 || obj.i == 8;
+                   }
+               }).toArray();
     debug(arr);
     assert.eq(2, arr.length);
 
     debug("after indexed find");
 
-    for (i = 1000; i < 2000; i++)
+    for (let i = 1000; i < 2000; i++)
         t.save({
             i: i,
             z: "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
diff --git a/jstests/core/query/js/js4.js b/jstests/core/query/js/js4.js
index a8beab4a8f6..11e67b2cd2c 100644
--- a/jstests/core/query/js/js4.js
+++ b/jstests/core/query/js/js4.js
@@ -3,17 +3,10 @@
 //   requires_scripting,
 // ]
 
-t = db.jstests_js4;
+let t = db.jstests_js4;
 t.drop();
 
-real = {
-    a: 1,
-    b: "abc",
-    c: /abc/i,
-    d: new Date(111911100111),
-    e: null,
-    f: true
-};
+let real = {a: 1, b: "abc", c: /abc/i, d: new Date(111911100111), e: null, f: true};
 
 t.save(real);
 
diff --git a/jstests/core/query/js/js5.js b/jstests/core/query/js/js5.js
index 05071a2b6a6..f41a4de78d4 100644
--- a/jstests/core/query/js/js5.js
+++ b/jstests/core/query/js/js5.js
@@ -3,7 +3,7 @@
 //     requires_scripting
 // ]
 
-t = db.jstests_js5;
+let t = db.jstests_js5;
 t.drop();
 
 t.save({a: 1});
diff --git a/jstests/core/query/js/js8.js b/jstests/core/query/js/js8.js
index 4bdf942e2c6..19544649236 100644
--- a/jstests/core/query/js/js8.js
+++ b/jstests/core/query/js/js8.js
@@ -3,7 +3,7 @@
 //   requires_scripting,
 // ]
 
-t = db.jstests_js8;
+let t = db.jstests_js8;
 t.drop();
 
 t.save({a: 1, b: [2, 3, 4]});
diff --git a/jstests/core/query/mr/mr_bigobject.js b/jstests/core/query/mr/mr_bigobject.js
index 83089935f35..57d8283af23 100644
--- a/jstests/core/query/mr/mr_bigobject.js
+++ b/jstests/core/query/mr/mr_bigobject.js
@@ -37,7 +37,7 @@ assert.eq([{_id: 1, value: 1}], outputColl.find().toArray());
 
 // The reduce function processes the expected amount of data.
 reduceFn = function(k, v) {
-    total = 0;
+    let total = 0;
     for (let i = 0; i < v.length; i++) {
         const x = v[i];
         if (typeof (x) == "number")
diff --git a/jstests/core/query/mr/mr_reduce_merge_other_db.js b/jstests/core/query/mr/mr_reduce_merge_other_db.js
index 5c730ada182..78559f6788e 100644
--- a/jstests/core/query/mr/mr_reduce_merge_other_db.js
+++ b/jstests/core/query/mr/mr_reduce_merge_other_db.js
@@ -23,7 +23,7 @@ const outDb = db.getMongo().getDB(outDbStr);
 const outColl = outDb[outCollStr];
 
 const mapFn = function() {
-    for (i = 0; i < this.a.length; i++)
+    for (let i = 0; i < this.a.length; i++)
         emit(this.a[i], 1);
 };
 const reduceFn = function(k, vs) {
diff --git a/jstests/core/query/mr/mr_replace_into_other_db.js b/jstests/core/query/mr/mr_replace_into_other_db.js
index 010b9d114af..a807b01f968 100644
--- a/jstests/core/query/mr/mr_replace_into_other_db.js
+++ b/jstests/core/query/mr/mr_replace_into_other_db.js
@@ -25,7 +25,7 @@ assert.commandWorked(outDb.random_coll.insert({val: 1}));
 const outColl = outDb[outCollStr];
 
 const mapFn = function() {
-    for (i = 0; i < this.a.length; i++)
+    for (let i = 0; i < this.a.length; i++)
         emit(this.a[i], 1);
 };
 const reduceFn = function(k, vs) {
diff --git a/jstests/core/query/mr/mr_sort.js b/jstests/core/query/mr/mr_sort.js
index 11ced9f2722..b01eb832e71 100644
--- a/jstests/core/query/mr/mr_sort.js
+++ b/jstests/core/query/mr/mr_sort.js
@@ -11,7 +11,7 @@
 //   requires_scripting,
 // ]
 
-t = db.mr_sort;
+let t = db.mr_sort;
 t.drop();
 
 t.createIndex({x: 1});
@@ -27,15 +27,15 @@ t.insert({x: 7});
 t.insert({x: 5});
 t.insert({x: 6});
 
-m = function() {
+let m = function() {
     emit("a", this.x);
 };
 
-r = function(k, v) {
+let r = function(k, v) {
     return Array.sum(v);
 };
 
-out = db.mr_sort_out;
+let out = db.mr_sort_out;
 assert.commandWorked(t.mapReduce(m, r, out.getName()));
 assert.eq([{_id: "a", value: 55}], out.find().toArray(), "A1");
 out.drop();
diff --git a/jstests/core/query/ne/ne1.js b/jstests/core/query/ne/ne1.js
index 5069637eb30..5135294a433 100644
--- a/jstests/core/query/ne/ne1.js
+++ b/jstests/core/query/ne/ne1.js
@@ -1,4 +1,4 @@
-t = db.ne1;
+let t = db.ne1;
 t.drop();
 
 t.save({x: 1});
diff --git a/jstests/core/query/ne/ne2.js b/jstests/core/query/ne/ne2.js
index 8f2b3d52f4c..4c8654560d3 100644
--- a/jstests/core/query/ne/ne2.js
+++ b/jstests/core/query/ne/ne2.js
@@ -3,7 +3,7 @@
 //   assumes_read_concern_local,
 // ]
 
-t = db.jstests_ne2;
+let t = db.jstests_ne2;
 t.drop();
 t.createIndex({a: 1});
 
@@ -12,7 +12,7 @@ t.save({a: 0});
 t.save({a: 0});
 t.save({a: 0.5});
 
-e = t.find({a: {$ne: 0}}).explain(true);
+let e = t.find({a: {$ne: 0}}).explain(true);
 assert.eq(2, e.executionStats.nReturned, 'A');
 
 e = t.find({a: {$gt: -1, $lt: 1, $ne: 0}}).explain(true);
diff --git a/jstests/core/query/ne/ne3.js b/jstests/core/query/ne/ne3.js
index 5c38858c019..ccdb06a357f 100644
--- a/jstests/core/query/ne/ne3.js
+++ b/jstests/core/query/ne/ne3.js
@@ -1,6 +1,6 @@
 // don't allow most operators with regex
 
-t = db.jstests_ne3;
+let t = db.jstests_ne3;
 t.drop();
 
 assert.throws(function() {
diff --git a/jstests/core/query/nin/nin.js b/jstests/core/query/nin/nin.js
index b9887e48828..f327bb1315b 100644
--- a/jstests/core/query/nin/nin.js
+++ b/jstests/core/query/nin/nin.js
@@ -1,6 +1,6 @@
 // @tags: [requires_fastcount]
 
-t = db.jstests_nin;
+let t = db.jstests_nin;
 t.drop();
 
 function checkEqual(name, key, value) {
@@ -16,7 +16,7 @@ function checkEqual(name, key, value) {
                   " != " + t.find().count());
 }
 
-doTest = function(n) {
+let doTest = function(n) {
     t.save({a: [1, 2, 3]});
     t.save({a: [1, 2, 4]});
     t.save({a: [1, 8, 5]});
diff --git a/jstests/core/query/nin/nin2.js b/jstests/core/query/nin/nin2.js
index d134f5ad4a4..de373c71190 100644
--- a/jstests/core/query/nin/nin2.js
+++ b/jstests/core/query/nin/nin2.js
@@ -2,13 +2,13 @@
 
 // Check that $nin is the opposite of $in SERVER-3264
 
-t = db.jstests_nin2;
+let t = db.jstests_nin2;
 t.drop();
 
 // Check various operator types.
 function checkOperators(array, inMatches) {
-    inCount = inMatches ? 1 : 0;
-    notInCount = 1 - inCount;
+    let inCount = inMatches ? 1 : 0;
+    let notInCount = 1 - inCount;
     assert.eq(inCount, t.count({foo: {$in: array}}));
     assert.eq(notInCount, t.count({foo: {$not: {$in: array}}}));
     assert.eq(notInCount, t.count({foo: {$nin: array}}));
diff --git a/jstests/core/query/not/not1.js b/jstests/core/query/not/not1.js
index 0726895ebbd..8ccfeaf7d87 100644
--- a/jstests/core/query/not/not1.js
+++ b/jstests/core/query/not/not1.js
@@ -1,6 +1,6 @@
 // @tags: [requires_fastcount]
 
-t = db.not1;
+let t = db.not1;
 t.drop();
 
 t.insert({a: 1});
diff --git a/jstests/core/query/number/numberint.js b/jstests/core/query/number/numberint.js
index 55c923aea79..f6ed7b5b8d7 100644
--- a/jstests/core/query/number/numberint.js
+++ b/jstests/core/query/number/numberint.js
@@ -1,14 +1,14 @@
 assert.eq.automsg("0", "new NumberInt()");
 
-n = new NumberInt(4);
+let n = new NumberInt(4);
 assert.eq.automsg("4", "n");
 assert.eq.automsg("4", "n.toNumber()");
 assert.eq.automsg("8", "n + 4");
 assert.eq.automsg("'NumberInt(4)'", "n.toString()");
 assert.eq.automsg("'NumberInt(4)'", "tojson( n )");
-a = {};
+let a = {};
 a.a = n;
-p = tojson(a);
+let p = tojson(a);
 assert.eq.automsg("'{ \"a\" : NumberInt(4) }'", "p");
 
 assert.eq.automsg("NumberInt(4 )", "eval( tojson( NumberInt( 4 ) ) )");
@@ -63,12 +63,10 @@ assert(NumberInt(1), "to bool a");
 // assert( ! NumberInt( 0 ) , "to bool b" );
 
 // create doc with int value in db
-t = db.getCollection("numberint");
+let t = db.getCollection("numberint");
 t.drop();
 
-o = {
-    a: NumberInt(42)
-};
+let o = {a: NumberInt(42)};
 t.save(o);
 
 assert.eq(42, t.findOne().a, "save doc 1");
@@ -76,7 +74,7 @@ assert.eq(1, t.find({a: {$type: 16}}).count(), "save doc 2");
 assert.eq(0, t.find({a: {$type: 1}}).count(), "save doc 3");
 
 // roundtripping
-mod = t.findOne({a: 42});
+let mod = t.findOne({a: 42});
 mod.a += 10;
 mod.b = "foo";
 delete mod._id;
diff --git a/jstests/core/query/number/numberlong.js b/jstests/core/query/number/numberlong.js
index a7dfd014539..d3477fd9ce0 100644
--- a/jstests/core/query/number/numberlong.js
+++ b/jstests/core/query/number/numberlong.js
@@ -1,14 +1,14 @@
 assert.eq.automsg("0", "new NumberLong()");
 
-n = new NumberLong(4);
+let n = new NumberLong(4);
 assert.eq.automsg("4", "n");
 assert.eq.automsg("4", "n.toNumber()");
 assert.eq.automsg("8", "n + 4");
 assert.eq.automsg("'NumberLong(4)'", "n.toString()");
 assert.eq.automsg("'NumberLong(4)'", "tojson( n )");
-a = {};
+let a = {};
 a.a = n;
-p = tojson(a);
+let p = tojson(a);
 assert.eq.automsg("'{ \"a\" : NumberLong(4) }'", "p");
 
 assert.eq.automsg("NumberLong(4 )", "eval( tojson( NumberLong( 4 ) ) )");
diff --git a/jstests/core/query/number/numberlong2.js b/jstests/core/query/number/numberlong2.js
index be254027b79..6d04ddd84e9 100644
--- a/jstests/core/query/number/numberlong2.js
+++ b/jstests/core/query/number/numberlong2.js
@@ -4,7 +4,7 @@
 
 // Test precision of NumberLong values with v1 index code SERVER-3717
 
-t = db.jstests_numberlong2;
+let t = db.jstests_numberlong2;
 t.drop();
 
 t.createIndex({x: 1});
@@ -24,8 +24,8 @@ chk(NumberLong("4503599627370497"));
 
 t.remove({});
 
-s = "11235399833116571";
-for (i = 99; i >= 0; --i) {
+let s = "11235399833116571";
+for (let i = 99; i >= 0; --i) {
     t.save({x: NumberLong(s + i)});
 }
 
diff --git a/jstests/core/query/number/numberlong3.js b/jstests/core/query/number/numberlong3.js
index 0dabdec2a05..ac89075ee75 100644
--- a/jstests/core/query/number/numberlong3.js
+++ b/jstests/core/query/number/numberlong3.js
@@ -1,26 +1,26 @@
 // Test sorting with long longs and doubles - SERVER-3719
 
-t = db.jstests_numberlong3;
+let t = db.jstests_numberlong3;
 t.drop();
 
-s = "11235399833116571";
-for (i = 10; i >= 0; --i) {
-    n = NumberLong(s + i);
+let s = "11235399833116571";
+for (let i = 10; i >= 0; --i) {
+    let n = NumberLong(s + i);
     t.save({x: n});
     if (0) {  // SERVER-3719
         t.save({x: n.floatApprox});
     }
 }
 
-ret = t.find().sort({x: 1}).toArray().filter(function(x) {
+let ret = t.find().sort({x: 1}).toArray().filter(function(x) {
     return typeof (x.x.floatApprox) != 'undefined';
 });
 
 // printjson( ret );
 
-for (i = 1; i < ret.length; ++i) {
-    first = ret[i - 1].x.toString();
-    second = ret[i].x.toString();
+for (let i = 1; i < ret.length; ++i) {
+    let first = ret[i - 1].x.toString();
+    let second = ret[i].x.toString();
     if (first.length == second.length) {
         assert.lte(ret[i - 1].x.toString(), ret[i].x.toString());
     }
diff --git a/jstests/core/query/number/numberlong4.js b/jstests/core/query/number/numberlong4.js
index d7d73898b34..2cd381cc61c 100644
--- a/jstests/core/query/number/numberlong4.js
+++ b/jstests/core/query/number/numberlong4.js
@@ -1,7 +1,7 @@
 // Test handling of comparison between long longs and their double approximations in btrees -
 // SERVER-3719.
 
-t = db.jstests_numberlong4;
+let t = db.jstests_numberlong4;
 t.drop();
 
 if (0) {  // SERVER-3719
@@ -10,9 +10,9 @@ if (0) {  // SERVER-3719
 
     Random.setRandomSeed();
 
-    s = "11235399833116571";
-    for (i = 0; i < 10000; ++i) {
-        n = NumberLong(s + Random.randInt(10));
+    let s = "11235399833116571";
+    for (let i = 0; i < 10000; ++i) {
+        let n = NumberLong(s + Random.randInt(10));
         t.insert({x: (Random.randInt(2) ? n : n.floatApprox)});
     }
 
diff --git a/jstests/core/query/objid/objid1.js b/jstests/core/query/objid/objid1.js
index d08089c26db..5c252a9531d 100644
--- a/jstests/core/query/objid/objid1.js
+++ b/jstests/core/query/objid/objid1.js
@@ -1,18 +1,16 @@
-t = db.objid1;
+let t = db.objid1;
 t.drop();
 
-b = new ObjectId();
+let b = new ObjectId();
 assert(b.str, "A");
 
-a = new ObjectId(b.str);
+let a = new ObjectId(b.str);
 assert.eq(a.str, b.str, "B");
 
 t.save({a: a});
 assert(t.findOne().a.isObjectId, "C");
 assert.eq(a.str, t.findOne().a.str, "D");
 
-x = {
-    a: new ObjectId()
-};
+let x = {a: new ObjectId()};
 eval(" y = " + tojson(x));
 assert.eq(x.a.str, y.a.str, "E");
diff --git a/jstests/core/query/objid/objid2.js b/jstests/core/query/objid/objid2.js
index 247843b587b..d25b1a6d9dc 100644
--- a/jstests/core/query/objid/objid2.js
+++ b/jstests/core/query/objid/objid2.js
@@ -1,4 +1,4 @@
-t = db.objid2;
+let t = db.objid2;
 t.drop();
 
 t.save({_id: 517, a: "hello"});
diff --git a/jstests/core/query/objid/objid3.js b/jstests/core/query/objid/objid3.js
index 12d45530e52..79e495e25cb 100644
--- a/jstests/core/query/objid/objid3.js
+++ b/jstests/core/query/objid/objid3.js
@@ -1,4 +1,4 @@
-t = db.objid3;
+let t = db.objid3;
 t.drop();
 
 t.save({a: "bob", _id: 517});
diff --git a/jstests/core/query/objid/objid4.js b/jstests/core/query/objid/objid4.js
index 7513e077029..de82d397b58 100644
--- a/jstests/core/query/objid/objid4.js
+++ b/jstests/core/query/objid/objid4.js
@@ -1,13 +1,11 @@
-
-
-o = new ObjectId();
+let o = new ObjectId();
 assert(o.str);
 
-a = new ObjectId(o.str);
+let a = new ObjectId(o.str);
 assert.eq(o.str, a.str);
 assert.eq(a.str, a.str.toString());
 
-b = ObjectId(o.str);
+let b = ObjectId(o.str);
 assert.eq(o.str, b.str);
 assert.eq(b.str, b.str.toString());
 
diff --git a/jstests/core/query/objid/objid5.js b/jstests/core/query/objid/objid5.js
index c656b286f5b..c8599509c86 100644
--- a/jstests/core/query/objid/objid5.js
+++ b/jstests/core/query/objid/objid5.js
@@ -1,11 +1,11 @@
-t = db.objid5;
+let t = db.objid5;
 t.drop();
 
 t.save({_id: 5.5});
 assert.eq(18, Object.bsonsize(t.findOne()), "A");
 
-x = db.runCommand({features: 1});
-y = db.runCommand({features: 1, oidReset: 1});
+let x = db.runCommand({features: 1});
+let y = db.runCommand({features: 1, oidReset: 1});
 
 if (!x.ok)
     print("x: " + tojson(x));
diff --git a/jstests/core/query/objid/objid7.js b/jstests/core/query/objid/objid7.js
index 4c3505f8965..2fc289b6000 100644
--- a/jstests/core/query/objid/objid7.js
+++ b/jstests/core/query/objid/objid7.js
@@ -1,7 +1,6 @@
-
-a = new ObjectId("4c1a478603eba73620000000");
-b = new ObjectId("4c1a478603eba73620000000");
-c = new ObjectId();
+let a = new ObjectId("4c1a478603eba73620000000");
+let b = new ObjectId("4c1a478603eba73620000000");
+let c = new ObjectId();
 
 assert.eq(a.toString(), b.toString(), "A");
 assert.eq(a.toString(), "ObjectId(\"4c1a478603eba73620000000\")", "B");
diff --git a/jstests/core/query/or/or1.js b/jstests/core/query/or/or1.js
index d90947d5f87..df3f1eb0ac4 100644
--- a/jstests/core/query/or/or1.js
+++ b/jstests/core/query/or/or1.js
@@ -1,22 +1,22 @@
-t = db.jstests_or1;
+let t = db.jstests_or1;
 t.drop();
 
-checkArrs = function(a, b) {
+let checkArrs = function(a, b) {
     assert.eq(a.length, b.length);
-    aStr = [];
-    bStr = [];
+    let aStr = [];
+    let bStr = [];
     a.forEach(function(x) {
         aStr.push(tojson(x));
     });
     b.forEach(function(x) {
         bStr.push(tojson(x));
     });
-    for (i = 0; i < aStr.length; ++i) {
+    for (let i = 0; i < aStr.length; ++i) {
         assert.neq(-1, bStr.indexOf(aStr[i]));
     }
 };
 
-doTest = function() {
+let doTest = function() {
     t.save({_id: 0, a: 1});
     t.save({_id: 1, a: 2});
     t.save({_id: 2, b: 1});
@@ -36,10 +36,10 @@ doTest = function() {
         t.find({$or: ["a"]}).toArray();
     });
 
-    a1 = t.find({$or: [{a: 1}]}).toArray();
+    let a1 = t.find({$or: [{a: 1}]}).toArray();
     checkArrs([{_id: 0, a: 1}, {_id: 4, a: 1, b: 1}, {_id: 5, a: 1, b: 2}], a1);
 
-    a1b2 = t.find({$or: [{a: 1}, {b: 2}]}).toArray();
+    let a1b2 = t.find({$or: [{a: 1}, {b: 2}]}).toArray();
     checkArrs(
         [
             {_id: 0, a: 1},
diff --git a/jstests/core/query/or/or5.js b/jstests/core/query/or/or5.js
index 1843c3d6cb7..ba4f529359c 100644
--- a/jstests/core/query/or/or5.js
+++ b/jstests/core/query/or/or5.js
@@ -2,7 +2,7 @@
 //   requires_getmore,
 // ]
 
-t = db.jstests_or5;
+let t = db.jstests_or5;
 t.drop();
 
 t.createIndex({a: 1});
@@ -28,7 +28,7 @@ assert.eq.automsg("6", "t.find( {$or:[{a:6},{b:3},{c:4}]} ).toArray().length");
 assert.eq.automsg("6", "t.find( {$or:[{a:2},{b:6},{c:4}]} ).toArray().length");
 assert.eq.automsg("6", "t.find( {$or:[{a:2},{b:3},{c:6}]} ).toArray().length");
 
-for (i = 2; i <= 7; ++i) {
+for (var i = 2; i <= 7; ++i) {
     assert.eq.automsg("7", "t.find( {$or:[{a:2},{b:3},{c:4}]} ).batchSize( i ).toArray().length");
     assert.eq.automsg("6", "t.find( {$or:[{a:6},{b:3},{c:4}]} ).batchSize( i ).toArray().length");
     assert.eq.automsg("6", "t.find( {$or:[{a:2},{b:6},{c:4}]} ).batchSize( i ).toArray().length");
diff --git a/jstests/core/query/or/or7.js b/jstests/core/query/or/or7.js
index e639a195739..414fbff858e 100644
--- a/jstests/core/query/or/or7.js
+++ b/jstests/core/query/or/or7.js
@@ -1,6 +1,6 @@
 // @tags: [requires_non_retryable_writes]
 
-t = db.jstests_or7;
+let t = db.jstests_or7;
 t.drop();
 
 t.createIndex({a: 1});
diff --git a/jstests/core/query/or/or8.js b/jstests/core/query/or/or8.js
index f33ef3146ce..00d1ea0cbed 100644
--- a/jstests/core/query/or/or8.js
+++ b/jstests/core/query/or/or8.js
@@ -4,7 +4,7 @@
 
 // missing collection
 
-t = db.jstests_or8;
+let t = db.jstests_or8;
 t.drop();
 
 t.find({"$or": [{"PropA": {"$lt": "b"}}, {"PropA": {"$lt": "b", "$gt": "a"}}]}).toArray();
diff --git a/jstests/core/query/or/or9.js b/jstests/core/query/or/or9.js
index 4938e84ca04..bcd527bb601 100644
--- a/jstests/core/query/or/or9.js
+++ b/jstests/core/query/or/or9.js
@@ -2,7 +2,7 @@
 
 // index skipping and previous index range negation
 
-t = db.jstests_or9;
+let t = db.jstests_or9;
 t.drop();
 
 t.createIndex({a: 1, b: 1});
diff --git a/jstests/core/query/or/orc.js b/jstests/core/query/or/orc.js
index 001d6f4bc9f..bb632e0ce6c 100644
--- a/jstests/core/query/or/orc.js
+++ b/jstests/core/query/or/orc.js
@@ -1,7 +1,7 @@
 // @tags: [requires_non_retryable_writes]
 
 // test that or duplicates are dropped in certain special cases
-t = db.jstests_orc;
+let t = db.jstests_orc;
 t.drop();
 
 // The goal here will be to ensure the full range of valid values is scanned for each or clause, in
diff --git a/jstests/core/query/or/ore.js b/jstests/core/query/or/ore.js
index 756db6215c5..775d5e3b2c1 100644
--- a/jstests/core/query/or/ore.js
+++ b/jstests/core/query/or/ore.js
@@ -1,7 +1,7 @@
 // verify that index direction is considered when deduping based on an earlier
 // index
 
-t = db.jstests_ore;
+let t = db.jstests_ore;
 t.drop();
 
 t.createIndex({a: -1});
diff --git a/jstests/core/query/or/org.js b/jstests/core/query/or/org.js
index 0c6808330c8..4780c54582b 100644
--- a/jstests/core/query/or/org.js
+++ b/jstests/core/query/or/org.js
@@ -2,7 +2,7 @@
 
 // SERVER-2282 $or de duping with sparse indexes
 
-t = db.jstests_org;
+let t = db.jstests_org;
 t.drop();
 
 t.createIndex({a: 1}, {sparse: true});
diff --git a/jstests/core/query/or/orh.js b/jstests/core/query/or/orh.js
index 91ce121e5a4..9a870cf27b1 100644
--- a/jstests/core/query/or/orh.js
+++ b/jstests/core/query/or/orh.js
@@ -2,7 +2,7 @@
 
 // SERVER-2831 Demonstration of sparse index matching semantics in a multi index $or query.
 
-t = db.jstests_orh;
+let t = db.jstests_orh;
 t.drop();
 
 t.createIndex({a: 1}, {sparse: true});
diff --git a/jstests/core/query/or/orj.js b/jstests/core/query/or/orj.js
index 6aabb3c39c7..9ff2288dc6b 100644
--- a/jstests/core/query/or/orj.js
+++ b/jstests/core/query/or/orj.js
@@ -1,6 +1,6 @@
 // Test nested $or clauses SERVER-2585 SERVER-3192
 
-t = db.jstests_orj;
+let t = db.jstests_orj;
 t.drop();
 
 t.save({a: 1, b: 2});
diff --git a/jstests/core/query/or/ork.js b/jstests/core/query/or/ork.js
index 8ce2346b6f3..525181f9061 100644
--- a/jstests/core/query/or/ork.js
+++ b/jstests/core/query/or/ork.js
@@ -1,6 +1,6 @@
 // SERVER-2585 Test $or clauses within indexed top level $or clauses.
 
-t = db.jstests_ork;
+let t = db.jstests_ork;
 t.drop();
 
 t.createIndex({a: 1});
diff --git a/jstests/core/query/or/oro.js b/jstests/core/query/or/oro.js
index 5ceda73818e..43bd0b87a81 100644
--- a/jstests/core/query/or/oro.js
+++ b/jstests/core/query/or/oro.js
@@ -5,26 +5,26 @@
 
 // Test $or query with several clauses on separate indexes.
 
-t = db.jstests_oro;
+let t = db.jstests_oro;
 t.drop();
 
-orClauses = [];
-for (idxKey = 'a'; idxKey <= 'aaaaaaaaaa'; idxKey += 'a') {
-    idx = {};
+let orClauses = [];
+for (let idxKey = 'a'; idxKey <= 'aaaaaaaaaa'; idxKey += 'a') {
+    let idx = {};
     idx[idxKey] = 1;
     t.createIndex(idx);
-    for (i = 0; i < 200; ++i) {
+    for (let i = 0; i < 200; ++i) {
         t.insert(idx);
     }
     orClauses.push(idx);
 }
 
 printjson(t.find({$or: orClauses}).explain());
-c = t.find({$or: orClauses}).batchSize(100);
-count = 0;
+let c = t.find({$or: orClauses}).batchSize(100);
+let count = 0;
 
 while (c.hasNext()) {
-    for (i = 0; i < 50 && c.hasNext(); ++i, c.next(), ++count)
+    for (let i = 0; i < 50 && c.hasNext(); ++i, c.next(), ++count)
         ;
     // Interleave with another operation.
     t.stats();
diff --git a/jstests/core/query/plan_cache/plan_cache_clear.js b/jstests/core/query/plan_cache/plan_cache_clear.js
index d03330ab08e..afc53155fd5 100644
--- a/jstests/core/query/plan_cache/plan_cache_clear.js
+++ b/jstests/core/query/plan_cache/plan_cache_clear.js
@@ -25,6 +25,7 @@
 'use strict';
 
 load("jstests/libs/sbe_util.js");  // For checkSBEEnabled.
+load("jstests/libs/fixture_helpers.js");
 
 const coll = db.jstests_plan_cache_clear;
 coll.drop();
@@ -228,8 +229,8 @@ assert.eq(0, numPlanCacheEntries(coll), dumpPlanCacheState(coll));
 //     Run reIndex on the collection.
 //     Confirm that cache is empty.
 // (Only standalone mode supports the reIndex command.)
-const isMongos = db.adminCommand({isdbgrid: 1}).isdbgrid;
-const isStandalone = !isMongos && !db.runCommand({hello: 1}).hasOwnProperty('setName');
+const isStandalone =
+    !FixtureHelpers.isMongos(db) && !db.runCommand({hello: 1}).hasOwnProperty('setName');
 if (isStandalone) {
     assert.eq(1, coll.find({a: 1, b: 1}).itcount());
     assert.eq(1, numPlanCacheEntries(coll), dumpPlanCacheState(coll));
diff --git a/jstests/core/query/project/proj_key1.js b/jstests/core/query/project/proj_key1.js
index c4834ffad49..0d6423156e0 100644
--- a/jstests/core/query/project/proj_key1.js
+++ b/jstests/core/query/project/proj_key1.js
@@ -2,12 +2,12 @@
 //   requires_getmore,
 // ]
 
-t = db.proj_key1;
+let t = db.proj_key1;
 t.drop();
 
-as = [];
+let as = [];
 
-for (i = 0; i < 10; i++) {
+for (let i = 0; i < 10; i++) {
     as.push({a: i});
     t.insert({a: i, b: i});
 }
diff --git a/jstests/core/query/pull/pull.js b/jstests/core/query/pull/pull.js
index 612c65f9e65..c5d1519f2aa 100644
--- a/jstests/core/query/pull/pull.js
+++ b/jstests/core/query/pull/pull.js
@@ -3,7 +3,7 @@
 // key.
 // @tags: [assumes_unsharded_collection]
 
-t = db.jstests_pull;
+let t = db.jstests_pull;
 t.drop();
 
 t.save({a: [1, 2, 3]});
diff --git a/jstests/core/query/pull/pull2.js b/jstests/core/query/pull/pull2.js
index a1b79955bb0..f3c04d517ca 100644
--- a/jstests/core/query/pull/pull2.js
+++ b/jstests/core/query/pull/pull2.js
@@ -3,7 +3,7 @@
 // key.
 // @tags: [assumes_unsharded_collection, requires_fastcount]
 
-t = db.pull2;
+let t = db.pull2;
 t.drop();
 
 t.save({a: [{x: 1}, {x: 1, b: 2}]});
diff --git a/jstests/core/query/pull/pull_or.js b/jstests/core/query/pull/pull_or.js
index 9ef1e091d29..42b0d93bb15 100644
--- a/jstests/core/query/pull/pull_or.js
+++ b/jstests/core/query/pull/pull_or.js
@@ -3,13 +3,10 @@
 // key.
 // @tags: [assumes_unsharded_collection]
 
-t = db.pull_or;
+let t = db.pull_or;
 t.drop();
 
-doc = {
-    _id: 1,
-    a: {b: [{x: 1}, {y: 'y'}, {x: 2}, {z: 'z'}]}
-};
+let doc = {_id: 1, a: {b: [{x: 1}, {y: 'y'}, {x: 2}, {z: 'z'}]}};
 
 t.insert(doc);
 
diff --git a/jstests/core/query/pull/pull_remove1.js b/jstests/core/query/pull/pull_remove1.js
index ab9368bab3b..307d84f2371 100644
--- a/jstests/core/query/pull/pull_remove1.js
+++ b/jstests/core/query/pull/pull_remove1.js
@@ -3,13 +3,10 @@
 // key.
 // @tags: [assumes_unsharded_collection]
 
-t = db.pull_remove1;
+let t = db.pull_remove1;
 t.drop();
 
-o = {
-    _id: 1,
-    a: [1, 2, 3, 4, 5, 6, 7, 8]
-};
+let o = {_id: 1, a: [1, 2, 3, 4, 5, 6, 7, 8]};
 t.insert(o);
 
 assert.eq(o, t.findOne(), "A1");
diff --git a/jstests/core/query/pull/pullall.js b/jstests/core/query/pull/pullall.js
index 2cd0872b079..7679bc6db71 100644
--- a/jstests/core/query/pull/pullall.js
+++ b/jstests/core/query/pull/pullall.js
@@ -3,7 +3,7 @@
 // key.
 // @tags: [assumes_unsharded_collection]
 
-t = db.jstests_pullall;
+let t = db.jstests_pullall;
 t.drop();
 
 t.save({a: [1, 2, 3]});
diff --git a/jstests/core/query/pull/pullall2.js b/jstests/core/query/pull/pullall2.js
index 10e8c89caa1..e1bc26cb0bd 100644
--- a/jstests/core/query/pull/pullall2.js
+++ b/jstests/core/query/pull/pullall2.js
@@ -3,14 +3,11 @@
 // key.
 // @tags: [assumes_unsharded_collection]
 
-t = db.pullall2;
+let t = db.pullall2;
 t.drop();
 
-o = {
-    _id: 1,
-    a: []
-};
-for (i = 0; i < 5; i++)
+let o = {_id: 1, a: []};
+for (let i = 0; i < 5; i++)
     o.a.push({x: i, y: i});
 
 t.insert(o);
diff --git a/jstests/core/query/push/push2.js b/jstests/core/query/push/push2.js
index 10669aa2581..0e00617b1ec 100644
--- a/jstests/core/query/push/push2.js
+++ b/jstests/core/query/push/push2.js
@@ -1,14 +1,14 @@
 (function() {
-t = db.push2;
+let t = db.push2;
 t.drop();
 
 t.save({_id: 1, a: []});
 
-s = new Array(700000).toString();
+let s = new Array(700000).toString();
 
-gotError = null;
+let gotError = null;
 
-for (x = 0; x < 100; x++) {
+for (let x = 0; x < 100; x++) {
     print(x + " pushes");
     var res = t.update({}, {$push: {a: s}});
     gotError = res.hasWriteError();
diff --git a/jstests/core/query/push/push_sort.js b/jstests/core/query/push/push_sort.js
index 2d74a3909f8..9ff12d5698c 100644
--- a/jstests/core/query/push/push_sort.js
+++ b/jstests/core/query/push/push_sort.js
@@ -7,7 +7,7 @@
 //  test exercises such $sort clause from the shell user's perspective.
 //
 
-t = db.push_sort;
+let t = db.push_sort;
 t.drop();
 
 //
diff --git a/jstests/core/query/query1.js b/jstests/core/query/query1.js
index 7e16a03a8fc..08a31d88502 100644
--- a/jstests/core/query/query1.js
+++ b/jstests/core/query/query1.js
@@ -1,14 +1,14 @@
 // @tags: [requires_fastcount]
 
-t = db.query1;
+let t = db.query1;
 t.drop();
 
 t.save({num: 1});
 t.save({num: 3});
 t.save({num: 4});
 
-num = 0;
-total = 0;
+let num = 0;
+let total = 0;
 
 t.find().forEach(function(z) {
     num++;
diff --git a/jstests/core/query/queryoptimizera.js b/jstests/core/query/queryoptimizera.js
index 2f3f2266847..42ca0032ea1 100644
--- a/jstests/core/query/queryoptimizera.js
+++ b/jstests/core/query/queryoptimizera.js
@@ -9,8 +9,8 @@
 // constraint is printed at appropriate times.  SERVER-5353
 
 function numWarnings() {
-    logs = db.adminCommand({getLog: "global"}).log;
-    ret = 0;
+    let logs = db.adminCommand({getLog: "global"}).log;
+    let ret = 0;
     logs.forEach(function(x) {
         if (x.match(warningMatchRegexp)) {
             ++ret;
@@ -19,23 +19,23 @@ function numWarnings() {
     return ret;
 }
 
-collectionNameIndex = 0;
+let collectionNameIndex = 0;
 
 // Generate a collection name not already present in the log.
 do {
-    testCollectionName = 'jstests_queryoptimizera__' + collectionNameIndex++;
-    warningMatchString =
+    var testCollectionName = 'jstests_queryoptimizera__' + collectionNameIndex++;
+    var warningMatchString =
         'unindexed _id query on capped collection.*collection: test.' + testCollectionName;
-    warningMatchRegexp = new RegExp(warningMatchString);
+    var warningMatchRegexp = new RegExp(warningMatchString);
 
 } while (numWarnings() > 0);
 
-t = db[testCollectionName];
+let t = db[testCollectionName];
 t.drop();
 
-notCappedCollectionName = testCollectionName + '_notCapped';
+let notCappedCollectionName = testCollectionName + '_notCapped';
 
-notCapped = db.getSiblingDB("local").getCollection(notCappedCollectionName);
+let notCapped = db.getSiblingDB("local").getCollection(notCappedCollectionName);
 notCapped.drop();
 
 assert.commandWorked(db.createCollection(testCollectionName, {capped: true, size: 1000}));
@@ -45,14 +45,14 @@ assert.commandWorked(
 t.insert({});
 notCapped.insert({});
 
-oldNumWarnings = 0;
+let oldNumWarnings = 0;
 
 function assertNoNewWarnings() {
     assert.eq(oldNumWarnings, numWarnings());
 }
 
 function assertNewWarning() {
-    newNumWarnings = numWarnings();
+    let newNumWarnings = numWarnings();
     // Ensure that newNumWarnings > oldNumWarnings.  It's not safe to test that oldNumWarnings + 1
     // == newNumWarnings, because a (simulated) page fault exception may cause multiple messages to
     // be logged instead of only one.
diff --git a/jstests/core/query/regex/regex.js b/jstests/core/query/regex/regex.js
index 363a03db20c..409c69b0b59 100644
--- a/jstests/core/query/regex/regex.js
+++ b/jstests/core/query/regex/regex.js
@@ -1,16 +1,13 @@
 // @tags: [
 //   assumes_read_concern_local,
 // ]
+load("jstests/libs/fixture_helpers.js");
 
 (function() {
 'use strict';
 
 const t = db.jstests_regex;
 
-const hello = db.runCommand("hello");
-assert.commandWorked(hello);
-const isMongos = (hello.msg === "isdbgrid");
-
 t.drop();
 assert.commandWorked(t.save({a: "bcd"}));
 assert.eq(1, t.count({a: /b/}), "A");
@@ -48,7 +45,7 @@ assert.eq(1, t.count(query));
 const result = t.find(query).explain();
 assert.commandWorked(result);
 
-if (!isMongos) {
+if (!FixtureHelpers.isMongos(db)) {
     assert(result.hasOwnProperty("queryPlanner"));
     assert(result.queryPlanner.hasOwnProperty("parsedQuery"), tojson(result));
     assert.eq(result.queryPlanner.parsedQuery, query);
diff --git a/jstests/core/query/regex/regex2.js b/jstests/core/query/regex/regex2.js
index 6ed1f2d290c..4801c7b8070 100644
--- a/jstests/core/query/regex/regex2.js
+++ b/jstests/core/query/regex/regex2.js
@@ -1,6 +1,6 @@
 // @tags: [requires_fastcount]
 
-t = db.regex2;
+let t = db.regex2;
 t.drop();
 
 assert.commandWorked(t.save({a: "test"}));
@@ -15,8 +15,8 @@ assert.eq(2, t.find({a: /test/i}).count(), "F");
 
 t.drop();
 
-a = "\u0442\u0435\u0441\u0442";
-b = "\u0422\u0435\u0441\u0442";
+let a = "\u0442\u0435\u0441\u0442";
+let b = "\u0422\u0435\u0441\u0442";
 
 assert((new RegExp(a)).test(a), "B 1");
 assert(!(new RegExp(a)).test(b), "B 2");
diff --git a/jstests/core/query/regex/regex3.js b/jstests/core/query/regex/regex3.js
index b21a7a81435..c84f64020e4 100644
--- a/jstests/core/query/regex/regex3.js
+++ b/jstests/core/query/regex/regex3.js
@@ -3,7 +3,7 @@
 //   assumes_read_concern_local,
 // ]
 
-t = db.regex3;
+let t = db.regex3;
 t.drop();
 
 assert.commandWorked(t.save({name: "eliot"}));
diff --git a/jstests/core/query/regex/regex4.js b/jstests/core/query/regex/regex4.js
index 0f7963fdd1e..d07614b1994 100644
--- a/jstests/core/query/regex/regex4.js
+++ b/jstests/core/query/regex/regex4.js
@@ -3,7 +3,7 @@
 //   assumes_read_concern_local,
 // ]
 
-t = db.regex4;
+let t = db.regex4;
 t.drop();
 
 assert.commandWorked(t.save({name: "eliot"}));
diff --git a/jstests/core/query/regex/regex5.js b/jstests/core/query/regex/regex5.js
index d0836a62686..ea32b4864df 100644
--- a/jstests/core/query/regex/regex5.js
+++ b/jstests/core/query/regex/regex5.js
@@ -1,5 +1,5 @@
 
-t = db.regex5;
+let t = db.regex5;
 t.drop();
 
 // Add filler data to make sure that indexed solutions are
@@ -11,10 +11,10 @@ for (var i = 0; i < 10; i++) {
 t.save({x: ["abc", "xyz1"]});
 t.save({x: ["ac", "xyz2"]});
 
-a = /.*b.*c/;
-x = /.*y.*/;
+let a = /.*b.*c/;
+let x = /.*y.*/;
 
-doit = function() {
+let doit = function() {
     assert.eq(1, t.find({x: a}).count(), "A");
     assert.eq(2, t.find({x: x}).count(), "B");
     assert.eq(2, t.find({x: {$in: [x]}}).count(), "C");            // SERVER-322
diff --git a/jstests/core/query/regex/regex6.js b/jstests/core/query/regex/regex6.js
index cc7b507f610..168826bbae1 100644
--- a/jstests/core/query/regex/regex6.js
+++ b/jstests/core/query/regex/regex6.js
@@ -4,7 +4,7 @@
 // @tags: [
 //   assumes_unsharded_collection,
 // ]
-t = db.regex6;
+let t = db.regex6;
 t.drop();
 
 t.save({name: "eliot"});
diff --git a/jstests/core/query/regex/regex7.js b/jstests/core/query/regex/regex7.js
index d89f914af4a..9a7e6153f1a 100644
--- a/jstests/core/query/regex/regex7.js
+++ b/jstests/core/query/regex/regex7.js
@@ -1,4 +1,4 @@
-t = db.regex_matches_self;
+let t = db.regex_matches_self;
 t.drop();
 
 t.insert({r: /^a/});
diff --git a/jstests/core/query/regex/regex8.js b/jstests/core/query/regex/regex8.js
index 20164acf464..e57d01db067 100644
--- a/jstests/core/query/regex/regex8.js
+++ b/jstests/core/query/regex/regex8.js
@@ -1,4 +1,4 @@
-t = db.regex8;
+let t = db.regex8;
 t.drop();
 
 t.insert({_id: 1, a: "abc"});
diff --git a/jstests/core/query/regex/regex9.js b/jstests/core/query/regex/regex9.js
index 96188d689dc..497b1cbdabc 100644
--- a/jstests/core/query/regex/regex9.js
+++ b/jstests/core/query/regex/regex9.js
@@ -1,5 +1,5 @@
 
-t = db.regex9;
+let t = db.regex9;
 t.drop();
 
 t.insert({_id: 1, a: ["a", "b", "c"]});
diff --git a/jstests/core/query/regex/regex_embed1.js b/jstests/core/query/regex/regex_embed1.js
index 11d92a6f3dc..97a0cae6552 100644
--- a/jstests/core/query/regex/regex_embed1.js
+++ b/jstests/core/query/regex/regex_embed1.js
@@ -1,4 +1,4 @@
-t = db.regex_embed1;
+let t = db.regex_embed1;
 
 t.drop();
 
diff --git a/jstests/core/query/regex/regexa.js b/jstests/core/query/regex/regexa.js
index 694436e87a8..24ea8f90686 100644
--- a/jstests/core/query/regex/regexa.js
+++ b/jstests/core/query/regex/regexa.js
@@ -1,6 +1,6 @@
 // Test simple regex optimization with a regex | (bar) present - SERVER-3298
 
-t = db.jstests_regexa;
+let t = db.jstests_regexa;
 t.drop();
 
 function check() {
diff --git a/jstests/core/query/regex/regexb.js b/jstests/core/query/regex/regexb.js
index 09e3518728b..398b9c5b836 100644
--- a/jstests/core/query/regex/regexb.js
+++ b/jstests/core/query/regex/regexb.js
@@ -1,6 +1,6 @@
 // Test more than four regex expressions in a query -- SERVER-969
 
-t = db.jstests_regexb;
+let t = db.jstests_regexb;
 t.drop();
 
 t.save({a: 'a', b: 'b', c: 'c', d: 'd', e: 'e'});
diff --git a/jstests/core/query/rename/rename_operator.js b/jstests/core/query/rename/rename_operator.js
index e86cc077e65..71965f269bd 100644
--- a/jstests/core/query/rename/rename_operator.js
+++ b/jstests/core/query/rename/rename_operator.js
@@ -11,7 +11,7 @@
  * ]
  */
 
-t = db.jstests_rename_operator;
+let t = db.jstests_rename_operator;
 t.drop();
 
 function bad(f) {
diff --git a/jstests/core/query/rename/rename_operator_missing_source.js b/jstests/core/query/rename/rename_operator_missing_source.js
index ff219cda563..d9c087af9aa 100644
--- a/jstests/core/query/rename/rename_operator_missing_source.js
+++ b/jstests/core/query/rename/rename_operator_missing_source.js
@@ -8,7 +8,7 @@
  * ]
  */
 
-t = db.jstests_rename5;
+let t = db.jstests_rename5;
 t.drop();
 
 t.createIndex({a: 1});
diff --git a/jstests/core/query/set/set1.js b/jstests/core/query/set/set1.js
index bae41fc5803..6914ddc217f 100644
--- a/jstests/core/query/set/set1.js
+++ b/jstests/core/query/set/set1.js
@@ -1,5 +1,5 @@
 
-t = db.set1;
+let t = db.set1;
 t.drop();
 
 t.insert({_id: 1, emb: {}});
diff --git a/jstests/core/query/set/set2.js b/jstests/core/query/set/set2.js
index c5b6e1c9553..9f37dd1e6b3 100644
--- a/jstests/core/query/set/set2.js
+++ b/jstests/core/query/set/set2.js
@@ -1,5 +1,5 @@
 
-t = db.set2;
+let t = db.set2;
 t.drop();
 
 t.save({_id: 1, x: true, y: {x: true}});
diff --git a/jstests/core/query/set/set3.js b/jstests/core/query/set/set3.js
index 4af579fa0b9..6dab2e3df2b 100644
--- a/jstests/core/query/set/set3.js
+++ b/jstests/core/query/set/set3.js
@@ -3,12 +3,12 @@
 // key.
 // @tags: [assumes_unsharded_collection]
 
-t = db.set3;
+let t = db.set3;
 t.drop();
 
 t.insert({"test1": {"test2": {"abcdefghijklmnopqrstu": {"id": 1}}}});
 t.update({}, {"$set": {"test1.test2.abcdefghijklmnopqrstuvwxyz": {"id": 2}}});
 
-x = t.findOne();
+let x = t.findOne();
 assert.eq(1, x.test1.test2.abcdefghijklmnopqrstu.id, "A");
 assert.eq(2, x.test1.test2.abcdefghijklmnopqrstuvwxyz.id, "B");
diff --git a/jstests/core/query/set/set4.js b/jstests/core/query/set/set4.js
index 99c0913b977..c1ccb87d1a0 100644
--- a/jstests/core/query/set/set4.js
+++ b/jstests/core/query/set/set4.js
@@ -3,13 +3,10 @@
 // key.
 // @tags: [assumes_unsharded_collection]
 
-t = db.set4;
+let t = db.set4;
 t.drop();
 
-orig = {
-    _id: 1,
-    a: [{x: 1}]
-};
+let orig = {_id: 1, a: [{x: 1}]};
 t.insert(orig);
 
 t.update({}, {$set: {'a.0.x': 2, 'foo.bar': 3}});
diff --git a/jstests/core/query/set/set5.js b/jstests/core/query/set/set5.js
index a848899f4af..fbaa832c3a0 100644
--- a/jstests/core/query/set/set5.js
+++ b/jstests/core/query/set/set5.js
@@ -3,7 +3,7 @@
 // key.
 // @tags: [assumes_unsharded_collection]
 
-t = db.set5;
+let t = db.set5;
 t.drop();
 
 function check(want, err) {
diff --git a/jstests/core/query/set/set6.js b/jstests/core/query/set/set6.js
index 2f82eb40a68..ac96cee0228 100644
--- a/jstests/core/query/set/set6.js
+++ b/jstests/core/query/set/set6.js
@@ -3,13 +3,10 @@
 // key.
 // @tags: [assumes_unsharded_collection]
 
-t = db.set6;
+let t = db.set6;
 t.drop();
 
-x = {
-    _id: 1,
-    r: new DBRef("foo", new ObjectId())
-};
+let x = {_id: 1, r: new DBRef("foo", new ObjectId())};
 t.insert(x);
 assert.eq(x, t.findOne(), "A");
 
diff --git a/jstests/core/query/set/set7.js b/jstests/core/query/set/set7.js
index e1cdd0f3bf2..232e3de5f8d 100644
--- a/jstests/core/query/set/set7.js
+++ b/jstests/core/query/set/set7.js
@@ -9,7 +9,7 @@
 
 // test $set with array indicies
 
-t = db.jstests_set7;
+let t = db.jstests_set7;
 var res;
 
 t.drop();
diff --git a/jstests/core/query/sort/sort10.js b/jstests/core/query/sort/sort10.js
index 6819c76fa5b..4369a179fcf 100644
--- a/jstests/core/query/sort/sort10.js
+++ b/jstests/core/query/sort/sort10.js
@@ -2,7 +2,7 @@
 //
 // @tags: [requires_fastcount]
 
-t = db.sort10;
+let t = db.sort10;
 
 function checkSorting1(opts) {
     t.drop();
@@ -20,25 +20,26 @@ checkSorting1({});
 checkSorting1({"background": true});
 
 function checkSorting2(dates, sortOrder) {
-    cur = t.find().sort({x: sortOrder});
+    let cur = t.find().sort({x: sortOrder});
     assert.eq(dates.length, cur.count(), "Incorrect number of results returned");
-    index = 0;
+    let index = 0;
     while (cur.hasNext()) {
-        date = cur.next().x;
+        let date = cur.next().x;
         assert.eq(dates[index].valueOf(), date.valueOf());
         index++;
     }
 }
 
 t.drop();
-dates = [new Date(-5000000000000), new Date(5000000000000), new Date(0), new Date(5), new Date(-5)];
+let dates =
+    [new Date(-5000000000000), new Date(5000000000000), new Date(0), new Date(5), new Date(-5)];
 for (var i = 0; i < dates.length; i++) {
     t.insert({x: dates[i]});
 }
 dates.sort(function(a, b) {
     return a - b;
 });
-reverseDates = dates.slice(0).reverse();
+let reverseDates = dates.slice(0).reverse();
 
 checkSorting2(dates, 1);
 checkSorting2(reverseDates, -1);
diff --git a/jstests/core/query/sort/sort2.js b/jstests/core/query/sort/sort2.js
index 1d373193fcc..38dd69921c8 100644
--- a/jstests/core/query/sort/sort2.js
+++ b/jstests/core/query/sort/sort2.js
@@ -1,5 +1,5 @@
 // test sorting, mainly a test ver simple with no index
-t = db.sort2;
+let t = db.sort2;
 
 t.drop();
 t.save({x: 1, y: {a: 5, b: 4}});
diff --git a/jstests/core/query/sort/sort6.js b/jstests/core/query/sort/sort6.js
index f2658bbcbad..9198c2fc136 100644
--- a/jstests/core/query/sort/sort6.js
+++ b/jstests/core/query/sort/sort6.js
@@ -1,4 +1,4 @@
-t = db.sort6;
+let t = db.sort6;
 
 function get(x) {
     return t.find().sort({c: x}).map(function(z) {
diff --git a/jstests/core/query/sort/sort8.js b/jstests/core/query/sort/sort8.js
index fa0b0040de1..ab40d4578e3 100644
--- a/jstests/core/query/sort/sort8.js
+++ b/jstests/core/query/sort/sort8.js
@@ -1,15 +1,15 @@
 // Check sorting of arrays indexed by key SERVER-2884
 
-t = db.jstests_sort8;
+let t = db.jstests_sort8;
 t.drop();
 
 t.save({a: [1, 10]});
 t.save({a: 5});
-unindexedForward = t.find().sort({a: 1}).toArray();
-unindexedReverse = t.find().sort({a: -1}).toArray();
+let unindexedForward = t.find().sort({a: 1}).toArray();
+let unindexedReverse = t.find().sort({a: -1}).toArray();
 t.createIndex({a: 1});
-indexedForward = t.find().sort({a: 1}).hint({a: 1}).toArray();
-indexedReverse = t.find().sort({a: -1}).hint({a: 1}).toArray();
+let indexedForward = t.find().sort({a: 1}).hint({a: 1}).toArray();
+let indexedReverse = t.find().sort({a: -1}).hint({a: 1}).toArray();
 
 assert.eq(unindexedForward, indexedForward);
 assert.eq(unindexedReverse, indexedReverse);
diff --git a/jstests/core/query/sort/sort9.js b/jstests/core/query/sort/sort9.js
index 57496b40da1..a606ec237fb 100644
--- a/jstests/core/query/sort/sort9.js
+++ b/jstests/core/query/sort/sort9.js
@@ -1,6 +1,6 @@
 // Unindexed array sorting SERVER-2884
 
-t = db.jstests_sort9;
+let t = db.jstests_sort9;
 t.drop();
 
 t.save({a: []});
diff --git a/jstests/core/query/sort/sort_merge.js b/jstests/core/query/sort/sort_merge.js
index fe6e24917d7..6612f52a6d4 100644
--- a/jstests/core/query/sort/sort_merge.js
+++ b/jstests/core/query/sort/sort_merge.js
@@ -114,7 +114,7 @@ function runTest(sorts, filters, verifyCallback) {
             // Check that there are no duplicates.
             let ids = new Set();
             for (let doc of res) {
-                assert(!ids.has(doc._id), () => "Duplicate _id: " + tojson(_id));
+                assert(!ids.has(doc._id), () => "Duplicate _id: " + tojson(doc._id));
                 ids.add(doc._id);
             }
         }
diff --git a/jstests/core/query/sort/sort_merge_collation.js b/jstests/core/query/sort/sort_merge_collation.js
index 38e6f33d9da..e4714718a76 100644
--- a/jstests/core/query/sort/sort_merge_collation.js
+++ b/jstests/core/query/sort/sort_merge_collation.js
@@ -74,7 +74,7 @@ function runTest(sorts, filters) {
             // Check that there are no duplicates.
             let ids = new Set();
             for (let doc of res) {
-                assert(!ids.has(doc._id), () => "Duplicate _id: " + tojson(_id));
+                assert(!ids.has(doc._id), () => "Duplicate _id: " + tojson(doc._id));
                 ids.add(doc._id);
             }
         }
diff --git a/jstests/core/query/sort/sort_numeric.js b/jstests/core/query/sort/sort_numeric.js
index 5ff3e71a066..908a9e7184a 100644
--- a/jstests/core/query/sort/sort_numeric.js
+++ b/jstests/core/query/sort/sort_numeric.js
@@ -1,5 +1,5 @@
 
-t = db.sort_numeric;
+let t = db.sort_numeric;
 t.drop();
 
 // there are two numeric types int he db; make sure it handles them right
@@ -18,7 +18,7 @@ for (var pass = 0; pass < 2; pass++) {
     var c = t.find().sort({a: 1});
     var last = 0;
     while (c.hasNext()) {
-        current = c.next();
+        let current = c.next();
         assert(current.a > last);
         last = current.a;
     }
diff --git a/jstests/core/query/sort/sortd.js b/jstests/core/query/sort/sortd.js
index 525f08ea947..39aacb77331 100644
--- a/jstests/core/query/sort/sortd.js
+++ b/jstests/core/query/sort/sortd.js
@@ -4,12 +4,12 @@
 
 // Test sorting with dups and multiple candidate query plans.
 
-t = db.jstests_sortd;
+let t = db.jstests_sortd;
 
 function checkNumSorted(n, query) {
-    docs = query.toArray();
+    let docs = query.toArray();
     assert.eq(n, docs.length);
-    for (i = 1; i < docs.length; ++i) {
+    for (let i = 1; i < docs.length; ++i) {
         assert.lte(docs[i - 1].a, docs[i].a);
     }
 }
@@ -31,10 +31,10 @@ t.drop();
 
 t.save({a: 1});
 t.save({a: 10});
-for (i = 2; i <= 9; ++i) {
+for (let i = 2; i <= 9; ++i) {
     t.save({a: i});
 }
-for (i = 0; i < 30; ++i) {
+for (let i = 0; i < 30; ++i) {
     t.save({a: 100});
 }
 t.createIndex({a: 1});
@@ -49,10 +49,10 @@ t.drop();
 
 t.save({a: 1});
 t.save({a: 200});
-for (i = 2; i <= 199; ++i) {
+for (let i = 2; i <= 199; ++i) {
     t.save({a: i});
 }
-for (i = 0; i < 30; ++i) {
+for (let i = 0; i < 30; ++i) {
     t.save({a: 2000});
 }
 t.createIndex({a: 1});
@@ -65,7 +65,7 @@ checkNumSorted(200, t.find({a: {$gte: 0, $lte: 200}, b: null}).sort({a: 1}));
 
 t.drop();
 
-for (i = 399; i >= 0; --i) {
+for (let i = 399; i >= 0; --i) {
     t.save({a: i});
 }
 t.createIndex({a: 1});
diff --git a/jstests/core/query/sort/sortf.js b/jstests/core/query/sort/sortf.js
index b2506eff663..8efa55c794e 100644
--- a/jstests/core/query/sort/sortf.js
+++ b/jstests/core/query/sort/sortf.js
@@ -5,18 +5,18 @@
 // Unsorted plan on {a:1}, sorted plan on {b:1}.  The unsorted plan exhausts its memory limit before
 // the sorted plan is chosen by the query optimizer.
 
-t = db.jstests_sortf;
+let t = db.jstests_sortf;
 t.drop();
 
 t.createIndex({a: 1});
 t.createIndex({b: 1});
 
-for (i = 0; i < 100; ++i) {
+for (let i = 0; i < 100; ++i) {
     t.save({a: 0, b: 0});
 }
 
-big = new Array(10 * 1000 * 1000).toString();
-for (i = 0; i < 5; ++i) {
+let big = new Array(10 * 1000 * 1000).toString();
+for (let i = 0; i < 5; ++i) {
     t.save({a: 1, b: 1, big: big});
 }
 
diff --git a/jstests/core/query/sort/sorti.js b/jstests/core/query/sort/sorti.js
index e30739b4867..4816f83be7a 100644
--- a/jstests/core/query/sort/sorti.js
+++ b/jstests/core/query/sort/sorti.js
@@ -1,6 +1,6 @@
 // Check that a projection is applied after an in memory sort.
 
-t = db.jstests_sorti;
+let t = db.jstests_sorti;
 t.drop();
 
 t.save({a: 1, b: 0});
@@ -9,10 +9,10 @@ t.save({a: 2, b: 2});
 t.save({a: 4, b: 3});
 
 function checkBOrder(query) {
-    arr = query.toArray();
-    order = [];
-    for (i in arr) {
-        a = arr[i];
+    let arr = query.toArray();
+    let order = [];
+    for (let i in arr) {
+        let a = arr[i];
         order.push(a.b);
     }
     assert.eq([0, 2, 1, 3], order);
diff --git a/jstests/core/query/sort/sortk.js b/jstests/core/query/sort/sortk.js
index 1561d61675e..adb829d182d 100644
--- a/jstests/core/query/sort/sortk.js
+++ b/jstests/core/query/sort/sortk.js
@@ -8,7 +8,7 @@
 //   requires_scripting,
 // ]
 
-t = db.jstests_sortk;
+let t = db.jstests_sortk;
 t.drop();
 
 function resetCollection() {
@@ -25,7 +25,7 @@ resetCollection();
 t.createIndex({a: 1, b: 1});
 
 function simpleQuery(extraFields, sort, hint) {
-    query = {a: {$in: [1, 2]}};
+    let query = {a: {$in: [1, 2]}};
     Object.extend(query, extraFields);
     sort = sort || {b: 1};
     hint = hint || {a: 1, b: 1};
@@ -67,7 +67,7 @@ assert.eq(0, simpleQuery({}, {a: -1, b: 1}).limit(-1)[0].b);
 
 // Without a hint, multiple cursors are attempted.
 assert.eq(0, t.find({a: {$in: [1, 2]}}).sort({b: 1}).limit(-1)[0].b);
-explain = t.find({a: {$in: [1, 2]}}).sort({b: 1}).limit(-1).explain(true);
+let explain = t.find({a: {$in: [1, 2]}}).sort({b: 1}).limit(-1).explain(true);
 assert.eq(1, explain.executionStats.nReturned);
 
 // The expected first result now comes from the first interval.
diff --git a/jstests/core/query/type/type1.js b/jstests/core/query/type/type1.js
index 8066de2a5c4..49674d834ea 100644
--- a/jstests/core/query/type/type1.js
+++ b/jstests/core/query/type/type1.js
@@ -1,6 +1,6 @@
 // @tags: [requires_fastcount]
 
-t = db.type1;
+let t = db.type1;
 t.drop();
 
 t.save({x: 1.1});
diff --git a/jstests/core/query/type/type2.js b/jstests/core/query/type/type2.js
index b2b094d0652..701d99f816e 100644
--- a/jstests/core/query/type/type2.js
+++ b/jstests/core/query/type/type2.js
@@ -1,6 +1,6 @@
 // SERVER-1735 $type:10 matches null value, not missing value.
 
-t = db.jstests_type2;
+let t = db.jstests_type2;
 t.drop();
 
 t.save({a: null});
diff --git a/jstests/core/query/type/type3.js b/jstests/core/query/type/type3.js
index 8b4858662dd..14c7697bc66 100644
--- a/jstests/core/query/type/type3.js
+++ b/jstests/core/query/type/type3.js
@@ -4,7 +4,7 @@
 
 // Check query type bracketing SERVER-3222
 
-t = db.jstests_type3;
+let t = db.jstests_type3;
 t.drop();
 
 t.createIndex({a: 1});
diff --git a/jstests/core/query/unset/unset.js b/jstests/core/query/unset/unset.js
index 14e18229723..c8e6ca501ef 100644
--- a/jstests/core/query/unset/unset.js
+++ b/jstests/core/query/unset/unset.js
@@ -1,10 +1,7 @@
-t = db.unset;
+let t = db.unset;
 t.drop();
 
-orig = {
-    _id: 1,
-    emb: {}
-};
+let orig = {_id: 1, emb: {}};
 t.insert(orig);
 
 t.update({_id: 1}, {$unset: {'emb.a': 1}});
diff --git a/jstests/core/query/unset/unset2.js b/jstests/core/query/unset/unset2.js
index e120ae2b674..4d192c5211e 100644
--- a/jstests/core/query/unset/unset2.js
+++ b/jstests/core/query/unset/unset2.js
@@ -5,7 +5,7 @@
 
 var res;
 
-t = db.unset2;
+let t = db.unset2;
 t.drop();
 
 t.save({a: ["a", "b", "c", "d"]});
diff --git a/jstests/core/query/where/where1.js b/jstests/core/query/where/where1.js
index 1082bb902e8..d093388c3d1 100644
--- a/jstests/core/query/where/where1.js
+++ b/jstests/core/query/where/where1.js
@@ -3,7 +3,7 @@
 //   requires_scripting,
 // ]
 
-t = db.getCollection("where1");
+let t = db.getCollection("where1");
 t.drop();
 
 t.save({a: 1});
diff --git a/jstests/core/query/where/where2.js b/jstests/core/query/where/where2.js
index 6561c829353..12ba7382e3c 100644
--- a/jstests/core/query/where/where2.js
+++ b/jstests/core/query/where/where2.js
@@ -3,7 +3,7 @@
 //   requires_scripting,
 // ]
 
-t = db.getCollection("where2");
+let t = db.getCollection("where2");
 t.drop();
 
 t.save({a: 1});
diff --git a/jstests/core/query/where/where3.js b/jstests/core/query/where/where3.js
index ffbe690312c..3b48bab56f5 100644
--- a/jstests/core/query/where/where3.js
+++ b/jstests/core/query/where/where3.js
@@ -3,7 +3,7 @@
 //     requires_scripting
 // ]
 
-t = db.where3;
+let t = db.where3;
 t.drop();
 
 t.save({returned_date: 5});
diff --git a/jstests/core/role_management_helpers.js b/jstests/core/role_management_helpers.js
index 9fd3d28ce55..05e93f7a70d 100644
--- a/jstests/core/role_management_helpers.js
+++ b/jstests/core/role_management_helpers.js
@@ -13,7 +13,7 @@
 // It is not a comprehensive test of the functionality of the role manipulation commands
 
 function assertHasRole(rolesArray, roleName, roleDB) {
-    for (i in rolesArray) {
+    for (let i in rolesArray) {
         var curRole = rolesArray[i];
         if (curRole.role == roleName && curRole.db == roleDB) {
             return;
@@ -23,7 +23,7 @@ function assertHasRole(rolesArray, roleName, roleDB) {
 }
 
 function assertHasPrivilege(privilegeArray, privilege) {
-    for (i in privilegeArray) {
+    for (let i in privilegeArray) {
         var curPriv = privilegeArray[i];
         if (curPriv.resource.cluster == privilege.resource.cluster &&
             curPriv.resource.anyResource == privilege.resource.anyResource &&
@@ -31,7 +31,7 @@ function assertHasPrivilege(privilegeArray, privilege) {
             curPriv.resource.collection == privilege.resource.collection) {
             // Same resource
             assert.eq(curPriv.actions.length, privilege.actions.length);
-            for (k in curPriv.actions) {
+            for (let k in curPriv.actions) {
                 assert.eq(curPriv.actions[k], privilege.actions[k]);
             }
             return;
diff --git a/jstests/core/server1470.js b/jstests/core/server1470.js
index c3c7d47aaeb..bbca047d8ee 100644
--- a/jstests/core/server1470.js
+++ b/jstests/core/server1470.js
@@ -3,15 +3,12 @@
 // key.
 // @tags: [assumes_unsharded_collection, requires_multi_updates, requires_non_retryable_writes]
 
-t = db.server1470;
+let t = db.server1470;
 t.drop();
 
-q = {
-    "name": "first",
-    "pic": {"$ref": "foo", "$id": ObjectId("4c48d04cd33a5a92628c9af6")}
-};
+let q = {"name": "first", "pic": {"$ref": "foo", "$id": ObjectId("4c48d04cd33a5a92628c9af6")}};
 t.update(q, {$set: {x: 1}}, true, true);
-ref = t.findOne().pic;
+let ref = t.findOne().pic;
 assert.eq("object", typeof (ref));
 assert.eq(q.pic["$ref"], ref["$ref"]);
 assert.eq(q.pic["$id"], ref["$id"]);
diff --git a/jstests/core/server5346.js b/jstests/core/server5346.js
index 18f2f019e5e..f9ad6852961 100644
--- a/jstests/core/server5346.js
+++ b/jstests/core/server5346.js
@@ -1,11 +1,8 @@
 
-t = db.server5346;
+let t = db.server5346;
 t.drop();
 
-x = {
-    _id: 1,
-    versions: {}
-};
+let x = {_id: 1, versions: {}};
 t.insert(x);
 
 t.update({_id: 1}, {$inc: {"versions.2_01": 1}});
diff --git a/jstests/core/server7756.js b/jstests/core/server7756.js
index 844c3a40d4d..574e5587845 100644
--- a/jstests/core/server7756.js
+++ b/jstests/core/server7756.js
@@ -1,5 +1,5 @@
 
-t = db.server7756;
+let t = db.server7756;
 t.drop();
 
 t.save({a: [{1: 'x'}, 'y']});
diff --git a/jstests/core/server9385.js b/jstests/core/server9385.js
index 4eb11076139..3e8cd4c96bd 100644
--- a/jstests/core/server9385.js
+++ b/jstests/core/server9385.js
@@ -2,11 +2,11 @@
 //
 // @tags: [requires_fastcount]
 
-t = db.server9385;
+let t = db.server9385;
 t.drop();
 
 t.insert({_id: 1, x: 1});
-x = t.findOne();
+let x = t.findOne();
 x._id = 2;
 t.save(x);
 
diff --git a/jstests/core/shell/shell1.js b/jstests/core/shell/shell1.js
index 4fc4c3a1c15..cbe52f14401 100644
--- a/jstests/core/shell/shell1.js
+++ b/jstests/core/shell/shell1.js
@@ -1,4 +1,4 @@
-x = 1;
+let x = 1;
 
 shellHelper("show", "tables;");
 shellHelper("show", "tables");
diff --git a/jstests/core/shell/shellkillop.js b/jstests/core/shell/shellkillop.js
index 0ac2ad681ed..b6c3746e052 100644
--- a/jstests/core/shell/shellkillop.js
+++ b/jstests/core/shell/shellkillop.js
@@ -1,15 +1,15 @@
-baseName = "jstests_shellkillop";
+let baseName = "jstests_shellkillop";
 
 // 'retry' should be set to true in contexts where an exception should cause the test to be retried
 // rather than to fail.
-retry = false;
+let retry = false;
 
 function testShellAutokillop() {
     if (true) {  // toggle to disable test
         db[baseName].drop();
 
         print("shellkillop.js insert data");
-        for (i = 0; i < 100000; ++i) {
+        for (let i = 0; i < 100000; ++i) {
             db[baseName].insert({i: 1});
         }
         assert.eq(100000, db[baseName].count());
@@ -19,7 +19,7 @@ function testShellAutokillop() {
         var evalStr = "print('SKO subtask started'); db." + baseName +
             ".update( {}, {$set:{i:'abcdefghijkl'}}, false, true ); db." + baseName + ".count();";
         print("shellkillop.js evalStr:" + evalStr);
-        spawn = startMongoProgramNoConnect(
+        let spawn = startMongoProgramNoConnect(
             "mongo", "--autokillop", "--port", myPort(), "--eval", evalStr);
 
         sleep(100);
@@ -35,7 +35,7 @@ function testShellAutokillop() {
         print("count abcdefghijkl:" + db[baseName].find({i: 'abcdefghijkl'}).count());
 
         var inprog = db.currentOp().inprog;
-        for (i in inprog) {
+        for (let i in inprog) {
             if (inprog[i].ns == "test." + baseName)
                 throw Error("shellkillop.js op is still running: " + tojson(inprog[i]));
         }
diff --git a/jstests/core/show_record_id.js b/jstests/core/show_record_id.js
index 3af12d74d61..6bf75a42d37 100644
--- a/jstests/core/show_record_id.js
+++ b/jstests/core/show_record_id.js
@@ -8,8 +8,8 @@ var t = db.show_record_id;
 t.drop();
 
 function checkResults(arr) {
-    for (i in arr) {
-        a = arr[i];
+    for (let i in arr) {
+        let a = arr[i];
         assert(a['$recordId']);
     }
 }
diff --git a/jstests/core/splitvector.js b/jstests/core/splitvector.js
index 5c3c1b2e559..54d8112ab97 100644
--- a/jstests/core/splitvector.js
+++ b/jstests/core/splitvector.js
@@ -26,14 +26,14 @@
 //        e.g. 20000
 // @param maxChunkSize is in MBs.
 //
-assertChunkSizes = function(splitVec, numDocs, maxChunkSize, msg) {
+let assertChunkSizes = function(splitVec, numDocs, maxChunkSize, msg) {
     splitVec = [{x: -1}].concat(splitVec);
     splitVec.push({x: numDocs + 1});
-    for (i = 0; i < splitVec.length - 1; i++) {
-        min = splitVec[i];
-        max = splitVec[i + 1];
+    for (let i = 0; i < splitVec.length - 1; i++) {
+        let min = splitVec[i];
+        let max = splitVec[i + 1];
         var avgObjSize = db.jstests_splitvector.stats().avgObjSize;
-        size = db.runCommand({datasize: "test.jstests_splitvector", min: min, max: max}).size;
+        let size = db.runCommand({datasize: "test.jstests_splitvector", min: min, max: max}).size;
 
         // It is okay for the last chunk to be  smaller. A collection's size does not
         // need to be exactly a multiple of maxChunkSize.
@@ -90,7 +90,7 @@ let bulkInsertDocsFixedX = function(coll, numDocs, filler, xVal) {
 // -------------------------
 //  TESTS START HERE
 // -------------------------
-f = db.jstests_splitvector;
+let f = db.jstests_splitvector;
 resetCollection();
 
 // -------------------------
@@ -125,29 +125,30 @@ assert.eq(
 resetCollection();
 f.createIndex({x: 1});
 
+let filler;
 var case4 = function() {
     // Get baseline document size
     filler = "";
     while (filler.length < 500)
         filler += "a";
     f.save({x: 0, y: filler});
-    docSize = db.runCommand({datasize: "test.jstests_splitvector"}).size;
+    let docSize = db.runCommand({datasize: "test.jstests_splitvector"}).size;
     assert.gt(docSize, 500, "4a");
 
     // Fill collection and get split vector for 1MB maxChunkSize
     let numDocs = 4500;
     bulkInsertDocs(f, numDocs - 1, filler);  // 1 document was already inserted.
-    res = db.runCommand(
+    let res = db.runCommand(
         {splitVector: "test.jstests_splitvector", keyPattern: {x: 1}, maxChunkSize: 1});
 
     // splitVector aims at getting half-full chunks after split
-    factor = 0.5;
+    let factor = 0.5;
 
     assert.eq(true, res.ok, "4b");
     assert.close(
         numDocs * docSize / ((1 << 20) * factor), res.splitKeys.length, "num split keys", -1);
     assertChunkSizes(res.splitKeys, numDocs, (1 << 20) * factor, "4d");
-    for (i = 0; i < res.splitKeys.length; i++) {
+    for (let i = 0; i < res.splitKeys.length; i++) {
         assertFieldNamesMatch(res.splitKeys[i], {x: 1});
     }
 };
@@ -162,7 +163,7 @@ f.createIndex({x: 1});
 var case5 = function() {
     // Fill collection and get split vector for 1MB maxChunkSize
     bulkInsertDocs(f, 4499, filler);
-    res = db.runCommand({
+    let res = db.runCommand({
         splitVector: "test.jstests_splitvector",
         keyPattern: {x: 1},
         maxChunkSize: 1,
@@ -171,7 +172,7 @@ var case5 = function() {
 
     assert.eq(true, res.ok, "5a");
     assert.eq(1, res.splitKeys.length, "5b");
-    for (i = 0; i < res.splitKeys.length; i++) {
+    for (let i = 0; i < res.splitKeys.length; i++) {
         assertFieldNamesMatch(res.splitKeys[i], {x: 1});
     }
 };
@@ -186,7 +187,7 @@ f.createIndex({x: 1});
 var case6 = function() {
     // Fill collection and get split vector for 1MB maxChunkSize
     bulkInsertDocs(f, 1999, filler);
-    res = db.runCommand({
+    let res = db.runCommand({
         splitVector: "test.jstests_splitvector",
         keyPattern: {x: 1},
         maxChunkSize: 1,
@@ -195,7 +196,7 @@ var case6 = function() {
 
     assert.eq(true, res.ok, "6a");
     assert.eq(3, res.splitKeys.length, "6b");
-    for (i = 0; i < res.splitKeys.length; i++) {
+    for (let i = 0; i < res.splitKeys.length; i++) {
         assertFieldNamesMatch(res.splitKeys[i], {x: 1});
     }
 };
@@ -212,12 +213,12 @@ var case7 = function() {
     // Fill collection and get split vector for 1MB maxChunkSize
     bulkInsertDocsFixedX(f, 2099, filler, 1);
     bulkInsertDocsFixedX(f, 9, filler, 2);
-    res = db.runCommand(
+    let res = db.runCommand(
         {splitVector: "test.jstests_splitvector", keyPattern: {x: 1}, maxChunkSize: 1});
 
     assert.eq(true, res.ok, "7a");
     assert.eq(2, res.splitKeys[0].x, "7b");
-    for (i = 0; i < res.splitKeys.length; i++) {
+    for (let i = 0; i < res.splitKeys.length; i++) {
         assertFieldNamesMatch(res.splitKeys[i], {x: 1});
     }
 };
@@ -234,14 +235,14 @@ var case8 = function() {
     bulkInsertDocsFixedX(f, 9, filler, 1);
     bulkInsertDocsFixedX(f, 2099, filler, 2);
     bulkInsertDocsFixedX(f, 9, filler, 3);
-    res = db.runCommand(
+    let res = db.runCommand(
         {splitVector: "test.jstests_splitvector", keyPattern: {x: 1}, maxChunkSize: 1});
 
     assert.eq(true, res.ok, "8a");
     assert.eq(2, res.splitKeys.length, "8b");
     assert.eq(2, res.splitKeys[0].x, "8c");
     assert.eq(3, res.splitKeys[1].x, "8d");
-    for (i = 0; i < res.splitKeys.length; i++) {
+    for (let i = 0; i < res.splitKeys.length; i++) {
         assertFieldNamesMatch(res.splitKeys[i], {x: 1});
     }
 };
@@ -262,7 +263,7 @@ var case9 = function() {
     assert.eq(3, f.count());
     print(f.getFullName());
 
-    res = db.runCommand({splitVector: f.getFullName(), keyPattern: {x: 1}, force: true});
+    let res = db.runCommand({splitVector: f.getFullName(), keyPattern: {x: 1}, force: true});
 
     assert.eq(true, res.ok, "9a");
     assert.eq(1, res.splitKeys.length, "9b");
@@ -275,7 +276,7 @@ var case9 = function() {
         assert.eq(true, res.ok, "9a: " + tojson(res));
         assert.eq(1, res.splitKeys.length, "9b: " + tojson(res));
         assert.eq(2, res.splitKeys[0].x, "9c: " + tojson(res));
-        for (i = 0; i < res.splitKeys.length; i++) {
+        for (let i = 0; i < res.splitKeys.length; i++) {
             assertFieldNamesMatch(res.splitKeys[i], {x: 1});
         }
     }
diff --git a/jstests/core/stage_debug/stages_and_hash.js b/jstests/core/stage_debug/stages_and_hash.js
index 4e75dace007..741a6778ad6 100644
--- a/jstests/core/stage_debug/stages_and_hash.js
+++ b/jstests/core/stage_debug/stages_and_hash.js
@@ -6,7 +6,7 @@
 //   no_selinux,
 // ]
 
-t = db.stages_and_hashed;
+let t = db.stages_and_hashed;
 t.drop();
 
 var collname = "stages_and_hashed";
@@ -21,7 +21,7 @@ t.createIndex({bar: 1});
 t.createIndex({baz: 1});
 
 // Scan foo <= 20
-ixscan1 = {
+let ixscan1 = {
     ixscan: {
         args: {
             name: "stages_and_hashed",
@@ -36,7 +36,7 @@ ixscan1 = {
 };
 
 // Scan bar >= 40
-ixscan2 = {
+let ixscan2 = {
     ixscan: {
         args: {
             name: "stages_and_hashed",
@@ -52,15 +52,13 @@ ixscan2 = {
 
 // bar = 50 - foo
 // Intersection is (foo=0 bar=50, foo=1 bar=49, ..., foo=10 bar=40)
-andix1ix2 = {
-    andHash: {args: {nodes: [ixscan1, ixscan2]}}
-};
-res = db.runCommand({stageDebug: {plan: andix1ix2, collection: collname}});
+let andix1ix2 = {andHash: {args: {nodes: [ixscan1, ixscan2]}}};
+let res = db.runCommand({stageDebug: {plan: andix1ix2, collection: collname}});
 assert.eq(res.ok, 1);
 assert.eq(res.results.length, 11);
 
 // Filter predicates from 2 indices.  Tests that we union the idx info.
-andix1ix2filter = {
+let andix1ix2filter = {
     fetch: {
         filter: {bar: {$in: [45, 46, 48]}, foo: {$in: [4, 5, 6]}},
         args: {node: {andHash: {args: {nodes: [ixscan1, ixscan2]}}}}
diff --git a/jstests/core/stage_debug/stages_and_sorted.js b/jstests/core/stage_debug/stages_and_sorted.js
index 34826baaa32..55c5abd8676 100644
--- a/jstests/core/stage_debug/stages_and_sorted.js
+++ b/jstests/core/stage_debug/stages_and_sorted.js
@@ -6,7 +6,7 @@
 //   no_selinux,
 // ]
 
-t = db.stages_and_sorted;
+let t = db.stages_and_sorted;
 t.drop();
 var collname = "stages_and_sorted";
 
@@ -31,7 +31,7 @@ t.createIndex({bar: 1});
 t.createIndex({baz: 1});
 
 // Scan foo == 1
-ixscan1 = {
+let ixscan1 = {
     ixscan: {
         args: {
             name: "stages_and_sorted",
@@ -46,7 +46,7 @@ ixscan1 = {
 };
 
 // Scan bar == 1
-ixscan2 = {
+let ixscan2 = {
     ixscan: {
         args: {
             name: "stages_and_sorted",
@@ -61,7 +61,7 @@ ixscan2 = {
 };
 
 // Scan baz == 12
-ixscan3 = {
+let ixscan3 = {
     ixscan: {
         args: {
             name: "stages_and_sorted",
@@ -76,18 +76,14 @@ ixscan3 = {
 };
 
 // Intersect foo==1 with bar==1 with baz==12.
-andix1ix2 = {
-    andSorted: {args: {nodes: [ixscan1, ixscan2, ixscan3]}}
-};
-res = db.runCommand({stageDebug: {collection: collname, plan: andix1ix2}});
+let andix1ix2 = {andSorted: {args: {nodes: [ixscan1, ixscan2, ixscan3]}}};
+let res = db.runCommand({stageDebug: {collection: collname, plan: andix1ix2}});
 printjson(res);
 assert.eq(res.ok, 1);
 assert.eq(res.results.length, N);
 
 // Might as well make sure that hashed does the same thing.
-andix1ix2hash = {
-    andHash: {args: {nodes: [ixscan1, ixscan2, ixscan3]}}
-};
+let andix1ix2hash = {andHash: {args: {nodes: [ixscan1, ixscan2, ixscan3]}}};
 res = db.runCommand({stageDebug: {collection: collname, plan: andix1ix2hash}});
 assert.eq(res.ok, 1);
 assert.eq(res.results.length, N);
diff --git a/jstests/core/stage_debug/stages_collection_scan.js b/jstests/core/stage_debug/stages_collection_scan.js
index 08b3eb2eeb6..ce072ad68b4 100644
--- a/jstests/core/stage_debug/stages_collection_scan.js
+++ b/jstests/core/stage_debug/stages_collection_scan.js
@@ -8,7 +8,7 @@
 // ]
 
 // Test basic query stage collection scan functionality.
-t = db.stages_collection_scan;
+let t = db.stages_collection_scan;
 t.drop();
 var collname = "stages_collection_scan";
 
@@ -17,37 +17,29 @@ for (var i = 0; i < N; ++i) {
     t.insert({foo: i});
 }
 
-forward = {
-    cscan: {args: {direction: 1}}
-};
-res = db.runCommand({stageDebug: {collection: collname, plan: forward}});
+let forward = {cscan: {args: {direction: 1}}};
+let res = db.runCommand({stageDebug: {collection: collname, plan: forward}});
 assert.eq(res.ok, 1);
 assert.eq(res.results.length, N);
 assert.eq(res.results[0].foo, 0);
 assert.eq(res.results[49].foo, 49);
 
 // And, backwards.
-backward = {
-    cscan: {args: {direction: -1}}
-};
+let backward = {cscan: {args: {direction: -1}}};
 res = db.runCommand({stageDebug: {collection: collname, plan: backward}});
 assert.eq(res.ok, 1);
 assert.eq(res.results.length, N);
 assert.eq(res.results[0].foo, 49);
 assert.eq(res.results[49].foo, 0);
 
-forwardFiltered = {
-    cscan: {args: {direction: 1}, filter: {foo: {$lt: 25}}}
-};
+let forwardFiltered = {cscan: {args: {direction: 1}, filter: {foo: {$lt: 25}}}};
 res = db.runCommand({stageDebug: {collection: collname, plan: forwardFiltered}});
 assert.eq(res.ok, 1);
 assert.eq(res.results.length, 25);
 assert.eq(res.results[0].foo, 0);
 assert.eq(res.results[24].foo, 24);
 
-backwardFiltered = {
-    cscan: {args: {direction: -1}, filter: {foo: {$lt: 25}}}
-};
+let backwardFiltered = {cscan: {args: {direction: -1}, filter: {foo: {$lt: 25}}}};
 res = db.runCommand({stageDebug: {collection: collname, plan: backwardFiltered}});
 assert.eq(res.ok, 1);
 assert.eq(res.results.length, 25);
diff --git a/jstests/core/stage_debug/stages_fetch.js b/jstests/core/stage_debug/stages_fetch.js
index bdec393ce1c..30a7ef61ac6 100644
--- a/jstests/core/stage_debug/stages_fetch.js
+++ b/jstests/core/stage_debug/stages_fetch.js
@@ -7,7 +7,7 @@
 // ]
 
 // Test basic fetch functionality.
-t = db.stages_fetch;
+let t = db.stages_fetch;
 t.drop();
 var collname = "stages_fetch";
 
@@ -20,7 +20,7 @@ t.createIndex({foo: 1});
 
 // 20 <= foo <= 30
 // bar == 25 (not covered, should error.)
-ixscan1 = {
+let ixscan1 = {
     ixscan: {
         args: {
             keyPattern: {foo: 1},
@@ -33,11 +33,11 @@ ixscan1 = {
         filter: {bar: 25}
     }
 };
-res = db.runCommand({stageDebug: {collection: collname, plan: ixscan1}});
+let res = db.runCommand({stageDebug: {collection: collname, plan: ixscan1}});
 assert.eq(res.ok, 0);
 
 // Now, add a fetch.  We should be able to filter on the non-covered field since we fetched the obj.
-ixscan2 = {
+let ixscan2 = {
     ixscan: {
         args: {
             keyPattern: {foo: 1},
@@ -49,9 +49,7 @@ ixscan2 = {
         }
     }
 };
-fetch = {
-    fetch: {args: {node: ixscan2}, filter: {bar: 25}}
-};
+let fetch = {fetch: {args: {node: ixscan2}, filter: {bar: 25}}};
 res = db.runCommand({stageDebug: {collection: collname, plan: fetch}});
 printjson(res);
 assert.eq(res.ok, 1);
diff --git a/jstests/core/stage_debug/stages_ixscan.js b/jstests/core/stage_debug/stages_ixscan.js
index de345fabb02..eb4d3c641d1 100644
--- a/jstests/core/stage_debug/stages_ixscan.js
+++ b/jstests/core/stage_debug/stages_ixscan.js
@@ -7,7 +7,7 @@
 // ]
 
 // Test basic query stage index scan functionality.
-t = db.stages_ixscan;
+let t = db.stages_ixscan;
 t.drop();
 var collname = "stages_ixscan";
 
@@ -40,7 +40,7 @@ assert.commandFailed(db.runCommand({
 }));
 
 // foo <= 20
-ixscan1 = {
+let ixscan1 = {
     ixscan: {
         args: {
             keyPattern: {foo: 1},
diff --git a/jstests/core/stage_debug/stages_limit_skip.js b/jstests/core/stage_debug/stages_limit_skip.js
index 623e403c504..680ae9d682d 100644
--- a/jstests/core/stage_debug/stages_limit_skip.js
+++ b/jstests/core/stage_debug/stages_limit_skip.js
@@ -7,7 +7,7 @@
 // ]
 
 // Test limit and skip
-t = db.stages_limit_skip;
+let t = db.stages_limit_skip;
 t.drop();
 var collname = "stages_limit_skip";
 
@@ -20,7 +20,7 @@ t.createIndex({foo: 1});
 
 // foo <= 20, decreasing
 // Limit of 5 results.
-ixscan1 = {
+let ixscan1 = {
     ixscan: {
         args: {
             keyPattern: {foo: 1},
@@ -32,10 +32,8 @@ ixscan1 = {
         }
     }
 };
-limit1 = {
-    limit: {args: {node: ixscan1, num: 5}}
-};
-res = db.runCommand({stageDebug: {collection: collname, plan: limit1}});
+let limit1 = {limit: {args: {node: ixscan1, num: 5}}};
+let res = db.runCommand({stageDebug: {collection: collname, plan: limit1}});
 assert.eq(res.ok, 1);
 assert.eq(res.results.length, 5);
 assert.eq(res.results[0].foo, 20);
@@ -43,9 +41,7 @@ assert.eq(res.results[4].foo, 16);
 
 // foo <= 20, decreasing
 // Skip 5 results.
-skip1 = {
-    skip: {args: {node: ixscan1, num: 5}}
-};
+let skip1 = {skip: {args: {node: ixscan1, num: 5}}};
 res = db.runCommand({stageDebug: {collection: collname, plan: skip1}});
 assert.eq(res.ok, 1);
 assert.eq(res.results.length, 16);
diff --git a/jstests/core/stage_debug/stages_mergesort.js b/jstests/core/stage_debug/stages_mergesort.js
index c202a3ca827..b3203b98dac 100644
--- a/jstests/core/stage_debug/stages_mergesort.js
+++ b/jstests/core/stage_debug/stages_mergesort.js
@@ -7,7 +7,7 @@
 // ]
 
 // Test query stage merge sorting.
-t = db.stages_mergesort;
+let t = db.stages_mergesort;
 t.drop();
 var collname = "stages_mergesort";
 
@@ -22,7 +22,7 @@ t.createIndex({baz: 1, bar: 1});
 
 // foo == 1
 // We would (internally) use "": MinKey and "": MaxKey for the bar index bounds.
-ixscan1 = {
+let ixscan1 = {
     ixscan: {
         args: {
             keyPattern: {foo: 1, bar: 1},
@@ -35,7 +35,7 @@ ixscan1 = {
     }
 };
 // baz == 1
-ixscan2 = {
+let ixscan2 = {
     ixscan: {
         args: {
             keyPattern: {baz: 1, bar: 1},
@@ -48,10 +48,8 @@ ixscan2 = {
     }
 };
 
-mergesort = {
-    mergeSort: {args: {nodes: [ixscan1, ixscan2], pattern: {bar: 1}}}
-};
-res = db.runCommand({stageDebug: {plan: mergesort, collection: collname}});
+let mergesort = {mergeSort: {args: {nodes: [ixscan1, ixscan2], pattern: {bar: 1}}}};
+let res = db.runCommand({stageDebug: {plan: mergesort, collection: collname}});
 assert.eq(res.ok, 1);
 assert.eq(res.results.length, 2 * N);
 assert.eq(res.results[0].bar, 0);
diff --git a/jstests/core/stage_debug/stages_or.js b/jstests/core/stage_debug/stages_or.js
index 6eb2e9812fb..3c674c5f017 100644
--- a/jstests/core/stage_debug/stages_or.js
+++ b/jstests/core/stage_debug/stages_or.js
@@ -7,7 +7,7 @@
 // ]
 
 // Test basic OR functionality
-t = db.stages_or;
+let t = db.stages_or;
 t.drop();
 var collname = "stages_or";
 
@@ -21,7 +21,7 @@ t.createIndex({bar: 1});
 t.createIndex({baz: 1});
 
 // baz >= 40
-ixscan1 = {
+let ixscan1 = {
     ixscan: {
         args: {
             keyPattern: {baz: 1},
@@ -34,7 +34,7 @@ ixscan1 = {
     }
 };
 // foo >= 40
-ixscan2 = {
+let ixscan2 = {
     ixscan: {
         args: {
             keyPattern: {foo: 1},
@@ -48,17 +48,13 @@ ixscan2 = {
 };
 
 // OR of baz and foo.  Baz == foo and we dedup.
-orix1ix2 = {
-    or: {args: {nodes: [ixscan1, ixscan2], dedup: true}}
-};
-res = db.runCommand({stageDebug: {collection: collname, plan: orix1ix2}});
+let orix1ix2 = {or: {args: {nodes: [ixscan1, ixscan2], dedup: true}}};
+let res = db.runCommand({stageDebug: {collection: collname, plan: orix1ix2}});
 assert.eq(res.ok, 1);
 assert.eq(res.results.length, 10);
 
 // No deduping, 2x the results.
-orix1ix2nodd = {
-    or: {args: {nodes: [ixscan1, ixscan2], dedup: false}}
-};
+let orix1ix2nodd = {or: {args: {nodes: [ixscan1, ixscan2], dedup: false}}};
 res = db.runCommand({stageDebug: {collection: collname, plan: orix1ix2nodd}});
 assert.eq(res.ok, 1);
 assert.eq(res.results.length, 20);
diff --git a/jstests/core/stage_debug/stages_sort.js b/jstests/core/stage_debug/stages_sort.js
index 2fd682edc3c..a79b64bca0a 100644
--- a/jstests/core/stage_debug/stages_sort.js
+++ b/jstests/core/stage_debug/stages_sort.js
@@ -3,7 +3,7 @@
 // @tags: [not_allowed_with_security_token]
 
 if (false) {
-    t = db.stages_sort;
+    let t = db.stages_sort;
     t.drop();
 
     var N = 50;
@@ -14,7 +14,7 @@ if (false) {
     t.createIndex({foo: 1});
 
     // Foo <= 20, descending.
-    ixscan1 = {
+    let ixscan1 = {
         ixscan: {
             args: {
                 name: "stages_sort",
@@ -29,8 +29,8 @@ if (false) {
     };
 
     // Sort with foo ascending.
-    sort1 = {sort: {args: {node: ixscan1, pattern: {foo: 1}}}};
-    res = db.runCommand({stageDebug: sort1});
+    let sort1 = {sort: {args: {node: ixscan1, pattern: {foo: 1}}}};
+    let res = db.runCommand({stageDebug: sort1});
     assert.eq(res.ok, 1);
     assert.eq(res.results.length, 21);
     assert.eq(res.results[0].foo, 0);
diff --git a/jstests/core/string_with_nul_bytes.js b/jstests/core/string_with_nul_bytes.js
index e72cc0b6dc1..718a1364666 100644
--- a/jstests/core/string_with_nul_bytes.js
+++ b/jstests/core/string_with_nul_bytes.js
@@ -1,9 +1,9 @@
 // SERVER-6649 - issues round-tripping strings with embedded NUL bytes
 
-t = db.string_with_nul_bytes.js;
+let t = db.string_with_nul_bytes.js;
 t.drop();
 
-string = "string with a NUL (\0) byte";
+let string = "string with a NUL (\0) byte";
 t.insert({str: string});
 assert.eq(t.findOne().str, string);
 assert.eq(t.findOne().str.length, string.length);  // just to be sure
diff --git a/jstests/core/sub1.js b/jstests/core/sub1.js
index d42677f3266..f38c5ccc4a0 100644
--- a/jstests/core/sub1.js
+++ b/jstests/core/sub1.js
@@ -1,16 +1,13 @@
 // sub1.js
 
-t = db.sub1;
+let t = db.sub1;
 t.drop();
 
-x = {
-    a: 1,
-    b: {c: {d: 2}}
-};
+let x = {a: 1, b: {c: {d: 2}}};
 
 t.save(x);
 
-y = t.findOne();
+let y = t.findOne();
 
 assert.eq(1, y.a);
 assert.eq(2, y.b.c.d);
diff --git a/jstests/core/testminmax.js b/jstests/core/testminmax.js
index 3ebf0a13f3a..712b00f5151 100644
--- a/jstests/core/testminmax.js
+++ b/jstests/core/testminmax.js
@@ -1,6 +1,6 @@
 // @tags: [requires_fastcount]
 
-t = db.minmaxtest;
+let t = db.minmaxtest;
 t.drop();
 t.insert({
     "_id": "IBM.N|00001264779918428889",
diff --git a/jstests/core/timeseries/timeseries_groupby_reorder.js b/jstests/core/timeseries/timeseries_groupby_reorder.js
index c4c34bc1249..a4f80197f10 100644
--- a/jstests/core/timeseries/timeseries_groupby_reorder.js
+++ b/jstests/core/timeseries/timeseries_groupby_reorder.js
@@ -26,7 +26,7 @@ assert.commandWorked(coll.insert({_id: 0, t: t, b: 2, c: 2}));
 assert.commandWorked(coll.insert({_id: 0, t: t, b: 3, c: 3}));
 
 // Test reordering the groupby and internal unpack buckets.
-if (!isMongos(db)) {
+if (!FixtureHelpers.isMongos(db)) {
     const res = coll.explain("queryPlanner").aggregate([
         {$group: {_id: '$meta', accmin: {$min: '$b'}, accmax: {$max: '$c'}}}
     ]);
diff --git a/jstests/core/timeseries/timeseries_update_one.js b/jstests/core/timeseries/timeseries_update_one.js
index b53f645c5a0..2f9b45e9b83 100644
--- a/jstests/core/timeseries/timeseries_update_one.js
+++ b/jstests/core/timeseries/timeseries_update_one.js
@@ -248,7 +248,7 @@ function testUpdateOne({initialDocList, updateQuery, updateObj, resultDocList, n
     while (batchNum < 4) {
         let batch = [];
         for (let i = 0; i < 30; i++) {
-            const doc = {_id: i, [timeField]: ISODate(), value: "a".repeat(1000)};
+            const doc = {_id: i, [timeFieldName]: ISODate(), value: "a".repeat(1000)};
             batch.push(doc);
         }
 
@@ -257,7 +257,7 @@ function testUpdateOne({initialDocList, updateQuery, updateObj, resultDocList, n
     }
 
     // Update any of the measurements with a document which will exceed the 128000 byte threshold.
-    const chunkyDoc = {_id: 128000, [timeField]: ISODate(), value: "a".repeat(10000)};
+    const chunkyDoc = {_id: 128000, [timeFieldName]: ISODate(), value: "a".repeat(10000)};
     testUpdateOne({
         // initialDocList: We manually inserted measurements.
         updateQuery: {},
diff --git a/jstests/core/timeseries/timeseries_user_system_buckets.js b/jstests/core/timeseries/timeseries_user_system_buckets.js
index 02ae0cb8f59..6835fca1864 100644
--- a/jstests/core/timeseries/timeseries_user_system_buckets.js
+++ b/jstests/core/timeseries/timeseries_user_system_buckets.js
@@ -13,8 +13,8 @@
  *   requires_fcv_63
  * ]
  */
-userCollSystemBuckets = db.system.buckets.coll;
-userColl = db.coll;
+let userCollSystemBuckets = db.system.buckets.coll;
+let userColl = db.coll;
 
 userCollSystemBuckets.drop();
 userColl.drop();
@@ -25,10 +25,10 @@ assert.commandWorked(userCollSystemBuckets.insert({a: 1}));
 // A user collection with the same postfix should not be considered time series collection
 assert.commandWorked(userColl.insert({a: 2}));
 
-docs = userColl.find().toArray();
+let docs = userColl.find().toArray();
 assert.eq(1, docs.length);
 
-docsSystemBuckets = userCollSystemBuckets.find().toArray();
+let docsSystemBuckets = userCollSystemBuckets.find().toArray();
 assert.eq(1, docsSystemBuckets.length);
 
 userCollSystemBuckets.drop();
diff --git a/jstests/core/txns/commands_banning_txnnumber_outside_transactions.js b/jstests/core/txns/commands_banning_txnnumber_outside_transactions.js
index a32cc59e255..49f03c6fddc 100644
--- a/jstests/core/txns/commands_banning_txnnumber_outside_transactions.js
+++ b/jstests/core/txns/commands_banning_txnnumber_outside_transactions.js
@@ -11,7 +11,7 @@
 (function() {
 "use strict";
 
-const isMongos = assert.commandWorked(db.runCommand("hello")).msg === "isdbgrid";
+load("jstests/libs/fixture_helpers.js");
 
 const session = db.getMongo().startSession();
 const sessionDb = session.getDatabase("admin");
@@ -53,7 +53,7 @@ nonRetryableWriteCommands.forEach(function(command) {
         [50768, 50889]);
 });
 
-if (!isMongos) {
+if (!FixtureHelpers.isMongos(db)) {
     nonRetryableWriteCommandsMongodOnly.forEach(function(command) {
         jsTest.log("Testing command: " + tojson(command));
         assert.commandFailedWithCode(
diff --git a/jstests/core/txns/commands_not_allowed_in_txn.js b/jstests/core/txns/commands_not_allowed_in_txn.js
index a261b14a0be..45352c27109 100644
--- a/jstests/core/txns/commands_not_allowed_in_txn.js
+++ b/jstests/core/txns/commands_not_allowed_in_txn.js
@@ -29,7 +29,7 @@ const sessionOptions = {
 const session = db.getMongo().startSession(sessionOptions);
 const sessionDb = session.getDatabase(dbName);
 
-const isMongos = assert.commandWorked(db.runCommand("hello")).msg === "isdbgrid";
+const runningOnMongos = assert.commandWorked(db.runCommand("hello")).msg === "isdbgrid";
 
 assert.commandWorked(testDB.createCollection(testColl.getName(), {writeConcern: {w: "majority"}}));
 assert.commandWorked(testDB.runCommand({
@@ -69,7 +69,7 @@ function testCommand(command) {
     assert(res.errmsg.match(errmsgRegExp), res);
 
     // Mongos has special handling for commitTransaction to support commit recovery.
-    if (!isMongos) {
+    if (!runningOnMongos) {
         assert.commandFailedWithCode(sessionDb.adminCommand({
             commitTransaction: 1,
             txnNumber: NumberLong(txnNumber),
@@ -134,7 +134,7 @@ const commands = [
 ];
 
 // There is no applyOps command on mongos.
-if (!isMongos) {
+if (!runningOnMongos) {
     commands.push({
         applyOps: [{
             op: "u",
@@ -164,7 +164,7 @@ assert.commandFailedWithCode(sessionDb.runCommand({
                              ErrorCodes.OperationNotSupportedInTransaction);
 
 // Mongos has special handling for commitTransaction to support commit recovery.
-if (!isMongos) {
+if (!runningOnMongos) {
     // The failed find should abort the transaction so a commit should fail.
     assert.commandFailedWithCode(sessionDb.adminCommand({
         commitTransaction: 1,
diff --git a/jstests/core/txns/dbstats_not_blocked_by_txn.js b/jstests/core/txns/dbstats_not_blocked_by_txn.js
index 6555a216e14..3eaec86df82 100644
--- a/jstests/core/txns/dbstats_not_blocked_by_txn.js
+++ b/jstests/core/txns/dbstats_not_blocked_by_txn.js
@@ -7,6 +7,8 @@
  */
 (function() {
 "use strict";
+load("jstests/libs/fixture_helpers.js");
+
 var dbName = 'dbstats_not_blocked_by_txn';
 var mydb = db.getSiblingDB(dbName);
 
@@ -16,8 +18,7 @@ mydb.createCollection("foo", {writeConcern: {w: "majority"}});
 var session = db.getMongo().startSession();
 var sessionDb = session.getDatabase(dbName);
 
-const isMongos = assert.commandWorked(db.runCommand("hello")).msg === "isdbgrid";
-if (isMongos) {
+if (FixtureHelpers.isMongos(db)) {
     // Before starting the transaction below, access the collection so it can be implicitly
     // sharded and force all shards to refresh their database versions because the refresh
     // requires an exclusive lock and would block behind the transaction.
diff --git a/jstests/core/txns/list_collections_not_blocked_by_txn.js b/jstests/core/txns/list_collections_not_blocked_by_txn.js
index 1ef9bb17b38..7b615c076f8 100644
--- a/jstests/core/txns/list_collections_not_blocked_by_txn.js
+++ b/jstests/core/txns/list_collections_not_blocked_by_txn.js
@@ -9,6 +9,7 @@
 // TODO (SERVER-39704): Remove the following load after SERVER-397074 is completed
 // For withTxnAndAutoRetryOnMongos.
 load('jstests/libs/auto_retry_transaction_in_sharding.js');
+load("jstests/libs/fixture_helpers.js");
 
 var dbName = 'list_collections_not_blocked';
 var mydb = db.getSiblingDB(dbName);
@@ -19,8 +20,7 @@ mydb.foo.drop({writeConcern: {w: "majority"}});
 
 assert.commandWorked(mydb.createCollection("foo", {writeConcern: {w: "majority"}}));
 
-const isMongos = assert.commandWorked(db.runCommand("hello")).msg === "isdbgrid";
-if (isMongos) {
+if (FixtureHelpers.isMongos(db)) {
     // Before starting the transaction below, access the collection so it can be implicitly
     // sharded and force all shards to refresh their database versions because the refresh
     // requires an exclusive lock and would block behind the transaction.
diff --git a/jstests/core/txns/noop_createIndexes_not_blocked_by_txn.js b/jstests/core/txns/noop_createIndexes_not_blocked_by_txn.js
index 75310ac65d2..083a2b978cd 100644
--- a/jstests/core/txns/noop_createIndexes_not_blocked_by_txn.js
+++ b/jstests/core/txns/noop_createIndexes_not_blocked_by_txn.js
@@ -6,6 +6,7 @@
 // TODO(SERVER-39704): Remove the following load after SERVER-39704 is completed
 // For withTxnAndAutoRetryOnMongos.
 load('jstests/libs/auto_retry_transaction_in_sharding.js');
+load("jstests/libs/fixture_helpers.js");
 
 const dbName = 'noop_createIndexes_not_blocked';
 const collName = 'test';
@@ -16,8 +17,7 @@ testDB.runCommand({drop: collName, writeConcern: {w: "majority"}});
 const session = db.getMongo().startSession({causalConsistency: false});
 const sessionDB = session.getDatabase(dbName);
 
-const isMongos = assert.commandWorked(db.runCommand("hello")).msg === "isdbgrid";
-if (isMongos) {
+if (FixtureHelpers.isMongos(db)) {
     // Access the collection before creating indexes so it can be implicitly sharded.
     assert.eq(sessionDB[collName].find().itcount(), 0);
 }
diff --git a/jstests/core/txns/statement_ids_accepted.js b/jstests/core/txns/statement_ids_accepted.js
index b5a56b31870..14e64897cf2 100644
--- a/jstests/core/txns/statement_ids_accepted.js
+++ b/jstests/core/txns/statement_ids_accepted.js
@@ -8,6 +8,7 @@
 //    # Tenant migrations don't support applyOps.
 //    tenant_migration_incompatible
 // ]
+load("jstests/libs/fixture_helpers.js");
 
 (function() {
 "use strict";
@@ -172,8 +173,7 @@ assert.commandWorked(sessionDb.adminCommand({
     autocommit: false
 }));
 
-const isMongos = assert.commandWorked(db.runCommand("hello")).msg === "isdbgrid";
-if (!isMongos) {
+if (!FixtureHelpers.isMongos(db)) {
     // Skip commands that do not exist on mongos.
 
     jsTestLog("Check that prepareTransaction accepts a statement ID");
diff --git a/jstests/core/views/invalid_system_views.js b/jstests/core/views/invalid_system_views.js
index 8c90068c81e..1844046056b 100644
--- a/jstests/core/views/invalid_system_views.js
+++ b/jstests/core/views/invalid_system_views.js
@@ -18,11 +18,12 @@
  *   uses_compact,
  * ]
  */
+load("jstests/libs/fixture_helpers.js");
 
 (function() {
 "use strict";
-const isMongos = db.runCommand({isdbgrid: 1}).isdbgrid;
-const isStandalone = !isMongos && !db.runCommand({hello: 1}).hasOwnProperty("setName");
+const runningOnMongos = FixtureHelpers.isMongos(db);
+const isStandalone = !runningOnMongos && !db.runCommand({hello: 1}).hasOwnProperty("setName");
 
 function runTest(badViewDefinition) {
     let viewsDB = db.getSiblingDB("invalid_system_views");
@@ -52,7 +53,7 @@ function runTest(badViewDefinition) {
             " in system.views";
     }
 
-    if (!isMongos) {
+    if (!runningOnMongos) {
         // Commands that run on existing regular collections should not be impacted by the
         // presence of invalid views. However, applyOps doesn't work on mongos.
         assert.commandWorked(
@@ -107,7 +108,7 @@ function runTest(badViewDefinition) {
     }
 
     const storageEngine = jsTest.options().storageEngine;
-    if (isMongos || storageEngine === "inMemory") {
+    if (runningOnMongos || storageEngine === "inMemory") {
         print("Not testing compact command on mongos or ephemeral storage engine");
     } else {
         assert.commandWorked(viewsDB.runCommand({compact: "collection", force: true}),
diff --git a/jstests/core/views/views_stats.js b/jstests/core/views/views_stats.js
index 3bda9eec250..623ef6b4dfd 100644
--- a/jstests/core/views/views_stats.js
+++ b/jstests/core/views/views_stats.js
@@ -17,6 +17,7 @@
 (function() {
 "use strict";
 load("jstests/libs/stats.js");
+load("jstests/libs/fixture_helpers.js");
 
 let viewsDB = db.getSiblingDB("views_stats");
 assert.commandWorked(viewsDB.dropDatabase());
@@ -42,9 +43,7 @@ lastHistogram = assertHistogramDiffEq(view, lastHistogram, 0, 1, 0);
 assert.writeError(view.update({}, {}));
 lastHistogram = assertHistogramDiffEq(view, lastHistogram, 0, 1, 0);
 
-let helloResponse = assert.commandWorked(viewsDB.runCommand("hello"));
-const isMongos = (helloResponse.msg === "isdbgrid");
-if (isMongos) {
+if (FixtureHelpers.isMongos(viewsDB)) {
     jsTest.log("Tests are being run on a mongos; skipping top tests.");
     return;
 }
diff --git a/jstests/core/write/autoid.js b/jstests/core/write/autoid.js
index 679b109fcc5..1797e3d7baf 100644
--- a/jstests/core/write/autoid.js
+++ b/jstests/core/write/autoid.js
@@ -3,14 +3,14 @@
 // key.
 // @tags: [assumes_unsharded_collection]
 
-f = db.jstests_autoid;
+let f = db.jstests_autoid;
 f.drop();
 
 f.save({z: 1});
-a = f.findOne({z: 1});
+let a = f.findOne({z: 1});
 f.update({z: 1}, {z: 2});
-b = f.findOne({z: 2});
+let b = f.findOne({z: 2});
 assert.eq(a._id.str, b._id.str);
-c = f.update({z: 2}, {z: "abcdefgabcdefgabcdefg"});
+let c = f.update({z: 2}, {z: "abcdefgabcdefgabcdefg"});
 c = f.findOne({});
 assert.eq(a._id.str, c._id.str);
diff --git a/jstests/core/write/batch_write_command_w0.js b/jstests/core/write/batch_write_command_w0.js
index 7d5038120b6..4b6bcb02168 100644
--- a/jstests/core/write/batch_write_command_w0.js
+++ b/jstests/core/write/batch_write_command_w0.js
@@ -33,12 +33,8 @@ coll.drop();
 //
 // Single document insert, w:0 write concern specified, missing ordered
 coll.drop();
-request = {
-    insert: coll.getName(),
-    documents: [{a: 1}],
-    writeConcern: {w: 0}
-};
-result = coll.runCommand(request);
+let request = {insert: coll.getName(), documents: [{a: 1}], writeConcern: {w: 0}};
+let result = coll.runCommand(request);
 assert.eq({ok: 1}, result);
 countEventually(coll, 1);
 
diff --git a/jstests/core/write/delete/remove.js b/jstests/core/write/delete/remove.js
index f08792aeca5..e3ecd634321 100644
--- a/jstests/core/write/delete/remove.js
+++ b/jstests/core/write/delete/remove.js
@@ -3,11 +3,11 @@
 // remove.js
 // unit test for db remove
 
-t = db.removetest;
+let t = db.removetest;
 
 function f(n, dir) {
     t.createIndex({x: dir || 1});
-    for (i = 0; i < n; i++)
+    for (let i = 0; i < n; i++)
         t.save({x: 3, z: "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"});
 
     assert.eq(n, t.find().count());
diff --git a/jstests/core/write/delete/remove3.js b/jstests/core/write/delete/remove3.js
index 6f0a94589e9..c2ce5ffead8 100644
--- a/jstests/core/write/delete/remove3.js
+++ b/jstests/core/write/delete/remove3.js
@@ -1,9 +1,9 @@
 // @tags: [requires_non_retryable_writes, requires_fastcount]
 
-t = db.remove3;
+let t = db.remove3;
 t.drop();
 
-for (i = 1; i <= 8; i++) {
+for (let i = 1; i <= 8; i++) {
     t.save({_id: i, x: i});
 }
 
diff --git a/jstests/core/write/delete/remove4.js b/jstests/core/write/delete/remove4.js
index 483de24bf7d..43dcbc5807b 100644
--- a/jstests/core/write/delete/remove4.js
+++ b/jstests/core/write/delete/remove4.js
@@ -1,6 +1,6 @@
 // @tags: [requires_non_retryable_writes]
 
-t = db.remove4;
+let t = db.remove4;
 t.drop();
 
 t.save({a: 1, b: 1});
diff --git a/jstests/core/write/delete/remove6.js b/jstests/core/write/delete/remove6.js
index f60200a8d81..0546fa3f8b6 100644
--- a/jstests/core/write/delete/remove6.js
+++ b/jstests/core/write/delete/remove6.js
@@ -1,9 +1,9 @@
 // @tags: [requires_non_retryable_writes, requires_fastcount]
 
-t = db.remove6;
+let t = db.remove6;
 t.drop();
 
-N = 1000;
+let N = 1000;
 
 function pop() {
     t.drop();
diff --git a/jstests/core/write/delete/remove7.js b/jstests/core/write/delete/remove7.js
index 9cc86329990..9924a34362c 100644
--- a/jstests/core/write/delete/remove7.js
+++ b/jstests/core/write/delete/remove7.js
@@ -1,6 +1,6 @@
 // @tags: [requires_non_retryable_writes]
 
-t = db.remove7;
+let t = db.remove7;
 t.drop();
 
 function getTags(n) {
@@ -14,13 +14,13 @@ function getTags(n) {
     return a;
 }
 
-for (i = 0; i < 1000; i++) {
+for (let i = 0; i < 1000; i++) {
     t.save({tags: getTags()});
 }
 
 t.createIndex({tags: 1});
 
-for (i = 0; i < 200; i++) {
+for (let i = 0; i < 200; i++) {
     for (var j = 0; j < 10; j++)
         t.save({tags: getTags(100)});
     var q = {tags: {$in: getTags(10)}};
diff --git a/jstests/core/write/delete/remove8.js b/jstests/core/write/delete/remove8.js
index 7a8263c21e4..3f34a753e92 100644
--- a/jstests/core/write/delete/remove8.js
+++ b/jstests/core/write/delete/remove8.js
@@ -4,10 +4,10 @@
 //   requires_fastcount,
 // ]
 
-t = db.remove8;
+let t = db.remove8;
 t.drop();
 
-N = 1000;
+let N = 1000;
 
 function fill() {
     for (var i = 0; i < N; i++) {
diff --git a/jstests/core/write/delete/remove_justone.js b/jstests/core/write/delete/remove_justone.js
index f5345627e34..1ae630432db 100644
--- a/jstests/core/write/delete/remove_justone.js
+++ b/jstests/core/write/delete/remove_justone.js
@@ -3,7 +3,7 @@
 // key.
 // @tags: [assumes_unsharded_collection, requires_non_retryable_writes, requires_fastcount]
 
-t = db.remove_justone;
+let t = db.remove_justone;
 t.drop();
 
 t.insert({x: 1});
diff --git a/jstests/core/write/delete/removec.js b/jstests/core/write/delete/removec.js
index 560f7405de3..bd68d43201c 100644
--- a/jstests/core/write/delete/removec.js
+++ b/jstests/core/write/delete/removec.js
@@ -6,36 +6,36 @@
 
 // Sanity test for removing documents with adjacent index keys.  SERVER-2008
 
-t = db.jstests_removec;
+let t = db.jstests_removec;
 t.drop();
 t.createIndex({a: 1});
 
 /** @return an array containing a sequence of numbers from i to i + 10. */
 function runStartingWith(i) {
-    ret = [];
-    for (j = 0; j < 11; ++j) {
+    let ret = [];
+    for (let j = 0; j < 11; ++j) {
         ret.push(i + j);
     }
     return ret;
 }
 
 // Insert some documents with adjacent index keys.
-for (i = 0; i < 1100; i += 11) {
+for (let i = 0; i < 1100; i += 11) {
     t.save({a: runStartingWith(i)});
 }
 
 // Remove and then reinsert random documents in the background.
-s = startParallelShell('t = db.jstests_removec;' +
-                       'Random.setRandomSeed();' +
-                       'for( j = 0; j < 1000; ++j ) {' +
-                       '    o = t.findOne( { a:Random.randInt( 1100 ) } );' +
-                       '    t.remove( { _id:o._id } );' +
-                       '    t.insert( o );' +
-                       '}');
+let s = startParallelShell('t = db.jstests_removec;' +
+                           'Random.setRandomSeed();' +
+                           'for( j = 0; j < 1000; ++j ) {' +
+                           '    o = t.findOne( { a:Random.randInt( 1100 ) } );' +
+                           '    t.remove( { _id:o._id } );' +
+                           '    t.insert( o );' +
+                           '}');
 
 // Find operations are error free. Note that the cursor throws if it detects the $err
 // field in the returned document.
-for (i = 0; i < 200; ++i) {
+for (let i = 0; i < 200; ++i) {
     t.find({a: {$gte: 0}}).hint({a: 1}).itcount();
 }
 
diff --git a/jstests/core/write/find_and_modify/find_and_modify.js b/jstests/core/write/find_and_modify/find_and_modify.js
index 56eae294568..47885cf9c92 100644
--- a/jstests/core/write/find_and_modify/find_and_modify.js
+++ b/jstests/core/write/find_and_modify/find_and_modify.js
@@ -6,7 +6,7 @@
 //   requires_fastcount,
 // ]
 
-t = db.find_and_modify;
+let t = db.find_and_modify;
 t.drop();
 
 // fill db
@@ -15,7 +15,8 @@ for (var i = 1; i <= 10; i++) {
 }
 
 // returns old
-out = t.findAndModify({sort: {priority: 1}, update: {$set: {inprogress: true}, $inc: {value: 1}}});
+let out =
+    t.findAndModify({sort: {priority: 1}, update: {$set: {inprogress: true}, $inc: {value: 1}}});
 assert.eq(out.value, 0);
 assert.eq(out.inprogress, false);
 t.update({_id: out._id}, {$set: {inprogress: false}});
@@ -133,7 +134,7 @@ runFindAndModify(true /* shouldMatch */, false /* upsert */, false /* new */);
 //
 
 t.drop();
-cmdRes = db.runCommand(
+let cmdRes = db.runCommand(
     {findAndModify: t.getName(), query: {_id: "miss"}, update: {$inc: {y: 1}}, upsert: true});
 assert.commandWorked(cmdRes);
 assert("value" in cmdRes);
diff --git a/jstests/core/write/find_and_modify/find_and_modify3.js b/jstests/core/write/find_and_modify/find_and_modify3.js
index a319aef7a2d..8aee710a0cf 100644
--- a/jstests/core/write/find_and_modify/find_and_modify3.js
+++ b/jstests/core/write/find_and_modify/find_and_modify3.js
@@ -3,7 +3,7 @@
 // key.
 // @tags: [assumes_unsharded_collection]
 
-t = db.find_and_modify3;
+let t = db.find_and_modify3;
 t.drop();
 
 t.insert({_id: 0, other: 0, comments: [{i: 0, j: 0}, {i: 1, j: 1}]});
@@ -14,10 +14,10 @@ t.insert({
 });  // this is the only one that gets modded
 t.insert({_id: 2, other: 2, comments: [{i: 0, j: 0}, {i: 1, j: 1}]});
 
-orig0 = t.findOne({_id: 0});
-orig2 = t.findOne({_id: 2});
+let orig0 = t.findOne({_id: 0});
+let orig2 = t.findOne({_id: 2});
 
-out = t.findAndModify({
+let out = t.findAndModify({
     query: {_id: 1, 'comments.i': 0},
     update: {$set: {'comments.$.j': 2}},
     'new': true,
diff --git a/jstests/core/write/find_and_modify/find_and_modify4.js b/jstests/core/write/find_and_modify/find_and_modify4.js
index d5b3ae23cb2..8d23edb62a9 100644
--- a/jstests/core/write/find_and_modify/find_and_modify4.js
+++ b/jstests/core/write/find_and_modify/find_and_modify4.js
@@ -3,7 +3,7 @@
 // key.
 // @tags: [assumes_unsharded_collection, requires_fastcount]
 
-t = db.find_and_modify4;
+let t = db.find_and_modify4;
 t.drop();
 
 // this is the best way to build auto-increment
diff --git a/jstests/core/write/find_and_modify/find_and_modify_server6254.js b/jstests/core/write/find_and_modify/find_and_modify_server6254.js
index 5a0dae9db22..2cb527446ba 100644
--- a/jstests/core/write/find_and_modify/find_and_modify_server6254.js
+++ b/jstests/core/write/find_and_modify/find_and_modify_server6254.js
@@ -3,11 +3,11 @@
 // key.
 // @tags: [assumes_unsharded_collection, requires_fastcount]
 
-t = db.find_and_modify_server6254;
+let t = db.find_and_modify_server6254;
 t.drop();
 
 t.insert({x: 1});
-ret = t.findAndModify({query: {x: 1}, update: {$set: {x: 2}}, new: true});
+let ret = t.findAndModify({query: {x: 1}, update: {$set: {x: 2}}, new: true});
 assert.eq(2, ret.x, tojson(ret));
 
 assert.eq(1, t.count());
diff --git a/jstests/core/write/find_and_modify/find_and_modify_server6582.js b/jstests/core/write/find_and_modify/find_and_modify_server6582.js
index 7ad8aebee76..2e5b38af2a2 100644
--- a/jstests/core/write/find_and_modify/find_and_modify_server6582.js
+++ b/jstests/core/write/find_and_modify/find_and_modify_server6582.js
@@ -3,11 +3,12 @@
 // key.
 // @tags: [assumes_unsharded_collection]
 
-t = db.find_and_modify_server6582;
+let t = db.find_and_modify_server6582;
 
 t.drop();
-x = t.runCommand("findAndModify", {query: {f: 1}, update: {$set: {f: 2}}, upsert: true, new: true});
-le = x.lastErrorObject;
+let x =
+    t.runCommand("findAndModify", {query: {f: 1}, update: {$set: {f: 2}}, upsert: true, new: true});
+let le = x.lastErrorObject;
 assert.eq(le.updatedExisting, false);
 assert.eq(le.n, 1);
 assert.eq(le.upserted, x.value._id);
diff --git a/jstests/core/write/find_and_modify/find_and_modify_server6588.js b/jstests/core/write/find_and_modify/find_and_modify_server6588.js
index 197c892ca67..344bb74a241 100644
--- a/jstests/core/write/find_and_modify/find_and_modify_server6588.js
+++ b/jstests/core/write/find_and_modify/find_and_modify_server6588.js
@@ -3,25 +3,12 @@
 // key.
 // @tags: [assumes_unsharded_collection]
 
-t = db.find_and_modify_sever6588;
+let t = db.find_and_modify_sever6588;
 
-initial = {
-    _id: 1,
-    a: [{b: 1}],
-    z: 1
-};
-up = {
-    "$set": {"a.$.b": 2}
-};
-q = {
-    _id: 1,
-    "a.b": 1
-};
-correct = {
-    _id: 1,
-    a: [{b: 2}],
-    z: 1
-};
+let initial = {_id: 1, a: [{b: 1}], z: 1};
+let up = {"$set": {"a.$.b": 2}};
+let q = {_id: 1, "a.b": 1};
+let correct = {_id: 1, a: [{b: 2}], z: 1};
 
 t.drop();
 t.insert(initial);
@@ -30,7 +17,7 @@ assert.eq(correct, t.findOne());
 
 t.drop();
 t.insert(initial);
-x = t.findAndModify({query: q, update: up});
+let x = t.findAndModify({query: q, update: up});
 assert.eq(correct, t.findOne());
 
 t.drop();
diff --git a/jstests/core/write/find_and_modify/find_and_modify_server6659.js b/jstests/core/write/find_and_modify/find_and_modify_server6659.js
index 029a32d6a49..091c9e93ebc 100644
--- a/jstests/core/write/find_and_modify/find_and_modify_server6659.js
+++ b/jstests/core/write/find_and_modify/find_and_modify_server6659.js
@@ -3,9 +3,9 @@
 // key.
 // @tags: [assumes_unsharded_collection]
 
-t = db.find_and_modify_server6659;
+let t = db.find_and_modify_server6659;
 t.drop();
 
-x = t.findAndModify({query: {f: 1}, update: {$set: {f: 2}}, upsert: true, new: true});
+let x = t.findAndModify({query: {f: 1}, update: {$set: {f: 2}}, upsert: true, new: true});
 assert.eq(2, x.f);
 assert.eq(2, t.findOne().f);
diff --git a/jstests/core/write/find_and_modify/find_and_modify_server6909.js b/jstests/core/write/find_and_modify/find_and_modify_server6909.js
index c74e342822b..24a62a9ba2b 100644
--- a/jstests/core/write/find_and_modify/find_and_modify_server6909.js
+++ b/jstests/core/write/find_and_modify/find_and_modify_server6909.js
@@ -3,12 +3,12 @@
 // key.
 // @tags: [assumes_unsharded_collection]
 
-c = db.find_and_modify_server6906;
+let c = db.find_and_modify_server6906;
 
 c.drop();
 
 c.insert({_id: 5, a: {b: 1}});
-ret = c.findAndModify({
+let ret = c.findAndModify({
     query: {'a.b': 1},
     update: {$set: {'a.b': 2}},  // Ensure the query on 'a.b' no longer matches.
     new: true
diff --git a/jstests/core/write/find_and_modify/find_and_modify_server6993.js b/jstests/core/write/find_and_modify/find_and_modify_server6993.js
index 4d9b169700d..eec75a9679b 100644
--- a/jstests/core/write/find_and_modify/find_and_modify_server6993.js
+++ b/jstests/core/write/find_and_modify/find_and_modify_server6993.js
@@ -3,7 +3,7 @@
 // key.
 // @tags: [assumes_unsharded_collection]
 
-c = db.find_and_modify_server6993;
+let c = db.find_and_modify_server6993;
 c.drop();
 
 c.insert({a: [1, 2]});
diff --git a/jstests/core/write/find_and_modify/find_and_modify_server7660.js b/jstests/core/write/find_and_modify/find_and_modify_server7660.js
index 7973279ddcf..3ec3d715405 100644
--- a/jstests/core/write/find_and_modify/find_and_modify_server7660.js
+++ b/jstests/core/write/find_and_modify/find_and_modify_server7660.js
@@ -3,13 +3,13 @@
 // key.
 // @tags: [assumes_unsharded_collection]
 
-t = db.find_and_modify_server7660;
+let t = db.find_and_modify_server7660;
 t.drop();
 
-a = t.findAndModify(
+let a = t.findAndModify(
     {query: {foo: 'bar'}, update: {$set: {bob: 'john'}}, sort: {foo: 1}, upsert: true, new: true});
 
-b = t.findOne();
+let b = t.findOne();
 assert.eq(a, b);
 assert.eq("bar", a.foo);
 assert.eq("john", a.bob);
diff --git a/jstests/core/write/find_and_modify/find_and_modify_where.js b/jstests/core/write/find_and_modify/find_and_modify_where.js
index 62375da7aab..6d605f9d23a 100644
--- a/jstests/core/write/find_and_modify/find_and_modify_where.js
+++ b/jstests/core/write/find_and_modify/find_and_modify_where.js
@@ -8,11 +8,11 @@
 //     requires_scripting,
 // ]
 
-t = db.find_and_modify_where;
+let t = db.find_and_modify_where;
 t.drop();
 
 t.insert({_id: 1, x: 1});
 
-res = t.findAndModify({query: {$where: "return this.x == 1"}, update: {$set: {y: 1}}});
+let res = t.findAndModify({query: {$where: "return this.x == 1"}, update: {$set: {y: 1}}});
 
 assert.eq(1, t.findOne().y);
diff --git a/jstests/core/write/insert/insert_id_undefined.js b/jstests/core/write/insert/insert_id_undefined.js
index 6d0bc38f8fb..80873def9c6 100644
--- a/jstests/core/write/insert/insert_id_undefined.js
+++ b/jstests/core/write/insert/insert_id_undefined.js
@@ -3,7 +3,7 @@
 // @tags: [assumes_no_implicit_collection_creation_after_drop, requires_fastcount]
 
 // ensure a document with _id undefined cannot be saved
-t = db.insert_id_undefined;
+let t = db.insert_id_undefined;
 t.drop();
 t.insert({_id: undefined});
 assert.eq(t.count(), 0);
diff --git a/jstests/core/write/update/update2.js b/jstests/core/write/update/update2.js
index 080875b50bd..a026346e355 100644
--- a/jstests/core/write/update/update2.js
+++ b/jstests/core/write/update/update2.js
@@ -3,7 +3,7 @@
 // key.
 // @tags: [assumes_unsharded_collection]
 
-f = db.ed_db_update2;
+let f = db.ed_db_update2;
 
 f.drop();
 f.save({a: 4});
diff --git a/jstests/core/write/update/update3.js b/jstests/core/write/update/update3.js
index 7e6c233e27a..884a65e9e0e 100644
--- a/jstests/core/write/update/update3.js
+++ b/jstests/core/write/update/update3.js
@@ -5,7 +5,7 @@
 
 // Update with mods corner cases.
 
-f = db.jstests_update3;
+let f = db.jstests_update3;
 
 f.drop();
 f.save({a: 1});
diff --git a/jstests/core/write/update/update5.js b/jstests/core/write/update/update5.js
index fafc0d72ce0..2bdcaea1ef2 100644
--- a/jstests/core/write/update/update5.js
+++ b/jstests/core/write/update/update5.js
@@ -4,7 +4,7 @@
 //
 // @tags: [assumes_unsharded_collection, requires_fastcount]
 
-t = db.update5;
+let t = db.update5;
 
 function go(key) {
     t.drop();
@@ -24,7 +24,7 @@ function go(key) {
     check(3, "C");
 
     var ik = {};
-    for (k in key)
+    for (let k in key)
         ik[k] = 1;
     t.createIndex(ik);
 
diff --git a/jstests/core/write/update/update6.js b/jstests/core/write/update/update6.js
index 8a1950b8d02..7704e921151 100644
--- a/jstests/core/write/update/update6.js
+++ b/jstests/core/write/update/update6.js
@@ -5,7 +5,7 @@
 //   assumes_unsharded_collection,
 // ]
 
-t = db.update6;
+let t = db.update6;
 t.drop();
 
 t.save({a: 1, b: {c: 1, d: 1}});
diff --git a/jstests/core/write/update/update7.js b/jstests/core/write/update/update7.js
index d3a7a5d1deb..a7fcbbfddf0 100644
--- a/jstests/core/write/update/update7.js
+++ b/jstests/core/write/update/update7.js
@@ -3,7 +3,7 @@
 // key.
 // @tags: [assumes_unsharded_collection, requires_multi_updates, requires_non_retryable_writes]
 
-t = db.update7;
+let t = db.update7;
 t.drop();
 
 function s() {
@@ -119,6 +119,7 @@ assert.eq("4,7,", s(), "E1");
 t.update({}, {$inc: {x: 1}}, false, true);
 assert.eq("5,8,1", s(), "E2");
 
+let i;
 for (i = 4; i < 8; i++)
     t.save({_id: i});
 t.save({_id: i, x: 1});
diff --git a/jstests/core/write/update/update8.js b/jstests/core/write/update/update8.js
index 596bc8695dd..7db54242cf3 100644
--- a/jstests/core/write/update/update8.js
+++ b/jstests/core/write/update/update8.js
@@ -1,5 +1,5 @@
 
-t = db.update8;
+let t = db.update8;
 t.drop();
 
 t.update({_id: 1, tags: {"$ne": "a"}}, {"$push": {tags: "a"}}, true);
diff --git a/jstests/core/write/update/update9.js b/jstests/core/write/update/update9.js
index d119681a09e..e7f9da8ddb6 100644
--- a/jstests/core/write/update/update9.js
+++ b/jstests/core/write/update/update9.js
@@ -1,8 +1,8 @@
 
-t = db.update9;
+let t = db.update9;
 t.drop();
 
-orig = {
+let orig = {
     "_id": 1,
     "question": "a",
     "choices": {"1": {"choice": "b"}, "0": {"choice": "c"}},
diff --git a/jstests/core/write/update/update_addToSet2.js b/jstests/core/write/update/update_addToSet2.js
index 44ba8bce671..2aabdb3078c 100644
--- a/jstests/core/write/update/update_addToSet2.js
+++ b/jstests/core/write/update/update_addToSet2.js
@@ -1,10 +1,8 @@
 
-t = db.update_addToSet2;
+let t = db.update_addToSet2;
 t.drop();
 
-o = {
-    _id: 1
-};
+let o = {_id: 1};
 t.insert({_id: 1});
 
 t.update({}, {$addToSet: {'kids': {'name': 'Bob', 'age': '4'}}});
diff --git a/jstests/core/write/update/update_addToSet3.js b/jstests/core/write/update/update_addToSet3.js
index efd682cef4c..ee13b651233 100644
--- a/jstests/core/write/update/update_addToSet3.js
+++ b/jstests/core/write/update/update_addToSet3.js
@@ -1,6 +1,6 @@
 // Test the use of $each in $addToSet
 
-t = db.update_addToSet3;
+let t = db.update_addToSet3;
 t.drop();
 
 t.insert({_id: 1});
diff --git a/jstests/core/write/update/update_arraymatch1.js b/jstests/core/write/update/update_arraymatch1.js
index 10b7e37e451..dd88af731aa 100644
--- a/jstests/core/write/update/update_arraymatch1.js
+++ b/jstests/core/write/update/update_arraymatch1.js
@@ -3,19 +3,14 @@
 // key.
 // @tags: [assumes_unsharded_collection]
 
-t = db.update_arraymatch1;
+let t = db.update_arraymatch1;
 t.drop();
 
-o = {
-    _id: 1,
-    a: [{x: 1, y: 1}, {x: 2, y: 2}, {x: 3, y: 3}]
-};
+let o = {_id: 1, a: [{x: 1, y: 1}, {x: 2, y: 2}, {x: 3, y: 3}]};
 t.insert(o);
 assert.eq(o, t.findOne(), "A1");
 
-q = {
-    "a.x": 2
-};
+let q = {"a.x": 2};
 t.update(q, {$set: {b: 5}});
 o.b = 5;
 assert.eq(o, t.findOne(), "A2");
diff --git a/jstests/core/write/update/update_arraymatch2.js b/jstests/core/write/update/update_arraymatch2.js
index 7610de7c962..5ec6be9e3cf 100644
--- a/jstests/core/write/update/update_arraymatch2.js
+++ b/jstests/core/write/update/update_arraymatch2.js
@@ -1,6 +1,6 @@
 // @tags: [requires_multi_updates, requires_non_retryable_writes]
 
-t = db.update_arraymatch2;
+let t = db.update_arraymatch2;
 t.drop();
 
 t.insert({});
diff --git a/jstests/core/write/update/update_arraymatch3.js b/jstests/core/write/update/update_arraymatch3.js
index 36f7ab22430..e16a518fd80 100644
--- a/jstests/core/write/update/update_arraymatch3.js
+++ b/jstests/core/write/update/update_arraymatch3.js
@@ -1,13 +1,9 @@
 // @tags: [requires_multi_updates, requires_non_retryable_writes]
 
-t = db.update_arraymatch3;
+let t = db.update_arraymatch3;
 t.drop();
 
-o = {
-    _id: 1,
-    title: "ABC",
-    comments: [{"by": "joe", "votes": 3}, {"by": "jane", "votes": 7}]
-};
+let o = {_id: 1, title: "ABC", comments: [{"by": "joe", "votes": 3}, {"by": "jane", "votes": 7}]};
 
 t.save(o);
 assert.eq(o, t.findOne(), "A1");
diff --git a/jstests/core/write/update/update_arraymatch4.js b/jstests/core/write/update/update_arraymatch4.js
index 3c087e53ca5..6c8f378fad1 100644
--- a/jstests/core/write/update/update_arraymatch4.js
+++ b/jstests/core/write/update/update_arraymatch4.js
@@ -3,13 +3,10 @@
 // key.
 // @tags: [assumes_unsharded_collection]
 
-t = db.update_arraymatch4;
+let t = db.update_arraymatch4;
 t.drop();
 
-x = {
-    _id: 1,
-    arr: ["A1", "B1", "C1"]
-};
+let x = {_id: 1, arr: ["A1", "B1", "C1"]};
 t.insert(x);
 assert.eq(x, t.findOne(), "A1");
 
diff --git a/jstests/core/write/update/update_arraymatch5.js b/jstests/core/write/update/update_arraymatch5.js
index 1b4c967b38b..0d676f3e4e5 100644
--- a/jstests/core/write/update/update_arraymatch5.js
+++ b/jstests/core/write/update/update_arraymatch5.js
@@ -4,7 +4,7 @@
 //   requires_non_retryable_writes,
 // ]
 
-t = db.update_arraymatch5;
+let t = db.update_arraymatch5;
 t.drop();
 
 t.insert({abc: {visible: true}, testarray: [{foobar_id: 316, visible: true, xxx: 1}]});
diff --git a/jstests/core/write/update/update_arraymatch6.js b/jstests/core/write/update/update_arraymatch6.js
index f8be918b826..16563e8d3e5 100644
--- a/jstests/core/write/update/update_arraymatch6.js
+++ b/jstests/core/write/update/update_arraymatch6.js
@@ -4,7 +4,7 @@
 // @tags: [assumes_unsharded_collection]
 
 var res;
-t = db.jstests_update_arraymatch6;
+let t = db.jstests_update_arraymatch6;
 t.drop();
 
 function doTest() {
diff --git a/jstests/core/write/update/update_arraymatch7.js b/jstests/core/write/update/update_arraymatch7.js
index cded4ba56f4..552c8469dd1 100644
--- a/jstests/core/write/update/update_arraymatch7.js
+++ b/jstests/core/write/update/update_arraymatch7.js
@@ -6,7 +6,7 @@
 // Check that the positional operator works properly when an index only match is used for the update
 // query spec.  SERVER-5067
 
-t = db.jstests_update_arraymatch7;
+let t = db.jstests_update_arraymatch7;
 t.drop();
 
 function testPositionalInc() {
diff --git a/jstests/core/write/update/update_arraymatch8.js b/jstests/core/write/update/update_arraymatch8.js
index e3aa91d6422..2f5365352e2 100644
--- a/jstests/core/write/update/update_arraymatch8.js
+++ b/jstests/core/write/update/update_arraymatch8.js
@@ -9,7 +9,7 @@
 // SERVER-7511
 
 // array.$.name
-t = db.jstests_update_arraymatch8;
+let t = db.jstests_update_arraymatch8;
 t.drop();
 t.createIndex({'array.name': 1});
 t.insert({'array': [{'name': 'old'}]});
@@ -51,7 +51,7 @@ assert(!t.findOne({'array.name': 'old'}));
 // // array.12.name
 t = db.jstests_update_arraymatch8;
 t.drop();
-arr = new Array();
+let arr = new Array();
 for (var i = 0; i < 20; i++) {
     arr.push({'name': 'old'});
 }
diff --git a/jstests/core/write/update/update_blank1.js b/jstests/core/write/update/update_blank1.js
index cd8f7433ebe..0e643f890b0 100644
--- a/jstests/core/write/update/update_blank1.js
+++ b/jstests/core/write/update/update_blank1.js
@@ -3,15 +3,10 @@
 // key.
 // @tags: [assumes_unsharded_collection]
 
-t = db.update_blank1;
+let t = db.update_blank1;
 t.drop();
 
-orig = {
-    "": 1,
-    _id: 2,
-    "a": 3,
-    "b": 4
-};
+let orig = {"": 1, _id: 2, "a": 3, "b": 4};
 t.insert(orig);
 var res = t.update({}, {$set: {"c": 5}});
 print(res);
diff --git a/jstests/core/write/update/update_dbref.js b/jstests/core/write/update/update_dbref.js
index f3e461c7379..caaff55cc91 100644
--- a/jstests/core/write/update/update_dbref.js
+++ b/jstests/core/write/update/update_dbref.js
@@ -8,7 +8,7 @@
 // Test that we can update DBRefs, but not dbref fields outside a DBRef
 
 var res;
-t = db.jstests_update_dbref;
+let t = db.jstests_update_dbref;
 t.drop();
 
 res = t.save({_id: 1, a: new DBRef("a", "b")});
diff --git a/jstests/core/write/update/update_invalid1.js b/jstests/core/write/update/update_invalid1.js
index bbda4cee53e..7276d33e5ef 100644
--- a/jstests/core/write/update/update_invalid1.js
+++ b/jstests/core/write/update/update_invalid1.js
@@ -2,7 +2,7 @@
 //   requires_fastcount,
 // ]
 
-t = db.update_invalid1;
+let t = db.update_invalid1;
 t.drop();
 
 t.update({_id: 5}, {$set: {$inc: {x: 5}}}, true);
diff --git a/jstests/core/write/update/update_multi3.js b/jstests/core/write/update/update_multi3.js
index 4c6769bc65a..463d4192ad9 100644
--- a/jstests/core/write/update/update_multi3.js
+++ b/jstests/core/write/update/update_multi3.js
@@ -1,6 +1,6 @@
 // @tags: [requires_multi_updates, requires_non_retryable_writes]
 
-t = db.update_multi3;
+let t = db.update_multi3;
 
 function test(useIndex) {
     t.drop();
@@ -8,7 +8,7 @@ function test(useIndex) {
     if (useIndex)
         t.createIndex({k: 1});
 
-    for (i = 0; i < 10; i++) {
+    for (let i = 0; i < 10; i++) {
         t.save({_id: i, k: 'x', a: []});
     }
 
diff --git a/jstests/core/write/update/update_multi4.js b/jstests/core/write/update/update_multi4.js
index cfe11616efc..d0e868ee5dd 100644
--- a/jstests/core/write/update/update_multi4.js
+++ b/jstests/core/write/update/update_multi4.js
@@ -1,9 +1,9 @@
 // @tags: [requires_multi_updates, requires_non_retryable_writes]
 
-t = db.update_mulit4;
+let t = db.update_mulit4;
 t.drop();
 
-for (i = 0; i < 1000; i++) {
+for (let i = 0; i < 1000; i++) {
     t.insert({_id: i, k: i % 12, v: "v" + i % 12});
 }
 
diff --git a/jstests/core/write/update/update_multi6.js b/jstests/core/write/update/update_multi6.js
index 023398534cd..217da4c002d 100644
--- a/jstests/core/write/update/update_multi6.js
+++ b/jstests/core/write/update/update_multi6.js
@@ -2,7 +2,7 @@
 
 var res;
 
-t = db.update_multi6;
+let t = db.update_multi6;
 t.drop();
 
 t.update({_id: 1}, {_id: 1, x: 1, y: 2}, true, false);
diff --git a/jstests/core/write/update/update_setOnInsert.js b/jstests/core/write/update/update_setOnInsert.js
index 9457c69f325..6e3f757660f 100644
--- a/jstests/core/write/update/update_setOnInsert.js
+++ b/jstests/core/write/update/update_setOnInsert.js
@@ -1,5 +1,5 @@
 // This tests that $setOnInsert works and allow setting the _id
-t = db.update_setOnInsert;
+let t = db.update_setOnInsert;
 var res;
 
 function dotest(useIndex) {
diff --git a/jstests/core/write/update/updatea.js b/jstests/core/write/update/updatea.js
index 99938c433fa..23dda37054b 100644
--- a/jstests/core/write/update/updatea.js
+++ b/jstests/core/write/update/updatea.js
@@ -4,13 +4,10 @@
 // @tags: [assumes_unsharded_collection]
 
 var res;
-t = db.updatea;
+let t = db.updatea;
 t.drop();
 
-orig = {
-    _id: 1,
-    a: [{x: 1, y: 2}, {x: 10, y: 11}]
-};
+let orig = {_id: 1, a: [{x: 1, y: 2}, {x: 10, y: 11}]};
 
 res = t.save(orig);
 assert.commandWorked(res);
@@ -52,7 +49,7 @@ orig = {
     _id: 1,
     a: []
 };
-for (i = 0; i < 12; i++)
+for (let i = 0; i < 12; i++)
     orig.a.push(i);
 
 res = t.save(orig);
diff --git a/jstests/core/write/update/updateb.js b/jstests/core/write/update/updateb.js
index 1518e7f3546..cea484a2732 100644
--- a/jstests/core/write/update/updateb.js
+++ b/jstests/core/write/update/updateb.js
@@ -3,15 +3,12 @@
 // key.
 // @tags: [assumes_unsharded_collection]
 
-t = db.updateb;
+let t = db.updateb;
 t.drop();
 
 t.update({"x.y": 2}, {$inc: {a: 7}}, true);
 
-correct = {
-    a: 7,
-    x: {y: 2}
-};
-got = t.findOne();
+let correct = {a: 7, x: {y: 2}};
+let got = t.findOne();
 delete got._id;
 assert.docEq(correct, got, "A");
diff --git a/jstests/core/write/update/updatec.js b/jstests/core/write/update/updatec.js
index 8ce8cf4ecdd..e47ed3ff797 100644
--- a/jstests/core/write/update/updatec.js
+++ b/jstests/core/write/update/updatec.js
@@ -1,5 +1,5 @@
 
-t = db.updatec;
+let t = db.updatec;
 t.drop();
 
 t.update({"_id": 123}, {$set: {"v": {"i": 123, "a": 456}}, $push: {"f": 234}}, 1, 0);
diff --git a/jstests/core/write/update/updated.js b/jstests/core/write/update/updated.js
index 919d02610c7..d850181afb5 100644
--- a/jstests/core/write/update/updated.js
+++ b/jstests/core/write/update/updated.js
@@ -3,13 +3,10 @@
 // key.
 // @tags: [assumes_unsharded_collection]
 
-t = db.updated;
+let t = db.updated;
 t.drop();
 
-o = {
-    _id: Math.random(),
-    items: [null, null, null, null]
-};
+let o = {_id: Math.random(), items: [null, null, null, null]};
 
 t.insert(o);
 assert.docEq(o, t.findOne(), "A1");
diff --git a/jstests/core/write/update/updatee.js b/jstests/core/write/update/updatee.js
index fbbcac01c9a..ed2c3a0d81c 100644
--- a/jstests/core/write/update/updatee.js
+++ b/jstests/core/write/update/updatee.js
@@ -5,7 +5,7 @@
 
 // big numeric updates (used to overflow)
 
-t = db.updatee;
+let t = db.updatee;
 t.drop();
 
 var o = {
diff --git a/jstests/core/write/update/updatef.js b/jstests/core/write/update/updatef.js
index 6597484f78a..3a55a38d954 100644
--- a/jstests/core/write/update/updatef.js
+++ b/jstests/core/write/update/updatef.js
@@ -7,24 +7,24 @@
 
 // Test unsafe management of nsdt on update command yield SERVER-3208
 
-prefixNS = db.jstests_updatef;
+let prefixNS = db.jstests_updatef;
 prefixNS.save({});
 
-t = db.jstests_updatef_actual;
+let t = db.jstests_updatef_actual;
 t.drop();
 
 t.save({a: 0, b: []});
-for (i = 0; i < 1000; ++i) {
+for (let i = 0; i < 1000; ++i) {
     t.save({a: 100});
 }
 t.save({a: 0, b: []});
 
 // Repeatedly rename jstests_updatef to jstests_updatef_ and back.  This will
 // invalidate the jstests_updatef_actual NamespaceDetailsTransient object.
-s = startParallelShell(
+let s = startParallelShell(
     "for( i=0; i < 100; ++i ) { db.jstests_updatef.renameCollection( 'jstests_updatef_' ); db.jstests_updatef_.renameCollection( 'jstests_updatef' ); }");
 
-for (i = 0; i < 20; ++i) {
+for (let i = 0; i < 20; ++i) {
     t.update({a: 0}, {$push: {b: i}}, false, true);
 }
 
diff --git a/jstests/core/write/update/updateg.js b/jstests/core/write/update/updateg.js
index 8a849a0ce59..b014547b3e2 100644
--- a/jstests/core/write/update/updateg.js
+++ b/jstests/core/write/update/updateg.js
@@ -5,7 +5,7 @@
 
 // SERVER-3370 check modifiers with field name characters comparing less than '.' character.
 
-t = db.jstests_updateg;
+let t = db.jstests_updateg;
 
 t.drop();
 t.update({}, {'$inc': {'all.t': 1, 'all-copy.t': 1}}, true);
diff --git a/jstests/core/write/update/updateh.js b/jstests/core/write/update/updateh.js
index 72d0d22c616..bafebc08ed7 100644
--- a/jstests/core/write/update/updateh.js
+++ b/jstests/core/write/update/updateh.js
@@ -7,7 +7,7 @@
 
 var res;
 
-t = db.jstest_updateh;
+let t = db.jstest_updateh;
 t.drop();
 
 t.insert({x: 1});
diff --git a/jstests/core/write/update/updatei.js b/jstests/core/write/update/updatei.js
index 599c9538a80..c5b7875df51 100644
--- a/jstests/core/write/update/updatei.js
+++ b/jstests/core/write/update/updatei.js
@@ -5,13 +5,13 @@
 
 // Test new (optional) update syntax
 // SERVER-4176
-t = db.updatei;
+let t = db.updatei;
 
 // Using a multi update
 
 t.drop();
 
-for (i = 0; i < 10; i++) {
+for (let i = 0; i < 10; i++) {
     t.save({_id: i, k: "x", a: []});
 }
 
@@ -24,7 +24,7 @@ t.drop();
 
 // Using a single update
 
-for (i = 0; i < 10; i++) {
+for (let i = 0; i < 10; i++) {
     t.save({_id: i, k: "x", a: []});
 }
 
@@ -35,7 +35,7 @@ t.drop();
 
 // Using upsert, found
 
-for (i = 0; i < 10; i++) {
+for (let i = 0; i < 10; i++) {
     t.save({_id: i, k: "x", a: []});
 }
 
@@ -46,7 +46,7 @@ t.drop();
 
 // Using upsert + multi, found
 
-for (i = 0; i < 10; i++) {
+for (let i = 0; i < 10; i++) {
     t.save({_id: i, k: "x", a: []});
 }
 
@@ -59,7 +59,7 @@ t.drop();
 
 // Using upsert, not found
 
-for (i = 0; i < 10; i++) {
+for (let i = 0; i < 10; i++) {
     t.save({_id: i, k: "x", a: []});
 }
 
@@ -70,7 +70,7 @@ t.drop();
 
 // Without upsert, found
 
-for (i = 0; i < 10; i++) {
+for (let i = 0; i < 10; i++) {
     t.save({_id: i, k: "x", a: []});
 }
 
@@ -81,7 +81,7 @@ t.drop();
 
 // Without upsert, not found
 
-for (i = 0; i < 10; i++) {
+for (let i = 0; i < 10; i++) {
     t.save({_id: i, k: "x", a: []});
 }
 
diff --git a/jstests/core/write/update/updatej.js b/jstests/core/write/update/updatej.js
index bab2a32f45f..77c5f52cbcf 100644
--- a/jstests/core/write/update/updatej.js
+++ b/jstests/core/write/update/updatej.js
@@ -5,7 +5,7 @@
 // encounters an error.
 // @tags: [requires_multi_updates, requires_non_retryable_writes, assumes_unsharded_collection]
 
-t = db.jstests_updatej;
+let t = db.jstests_updatej;
 t.drop();
 
 t.save({a: []});
diff --git a/jstests/core/write/update/updatek.js b/jstests/core/write/update/updatek.js
index 923b4145d1d..4ef4fe8ddb9 100644
--- a/jstests/core/write/update/updatek.js
+++ b/jstests/core/write/update/updatek.js
@@ -5,7 +5,7 @@
 
 // Test modifier operations on numerically equivalent string field names.  SERVER-4776
 
-t = db.jstests_updatek;
+let t = db.jstests_updatek;
 
 t.drop();
 t.save({_id: 0, '1': {}, '01': {}});
diff --git a/jstests/core/write/update/updatel.js b/jstests/core/write/update/updatel.js
index a663f306722..332fad0c6ec 100644
--- a/jstests/core/write/update/updatel.js
+++ b/jstests/core/write/update/updatel.js
@@ -8,7 +8,7 @@
 // setinel ('$'), the update fails with an error.  SERVER-6669 SERVER-4713
 
 var res;
-t = db.jstests_updatel;
+let t = db.jstests_updatel;
 t.drop();
 
 // The collection is empty, forcing an upsert.  In this case the query has no array position match
diff --git a/jstests/core/write/update/updatem.js b/jstests/core/write/update/updatem.js
index 8e4af7e56c7..0dd0fcba014 100644
--- a/jstests/core/write/update/updatem.js
+++ b/jstests/core/write/update/updatem.js
@@ -7,7 +7,7 @@
 
 // Tests that _id will exist in all updated docs.
 
-t = db.jstests_updatem;
+let t = db.jstests_updatem;
 t.drop();
 
 // new _id from insert (upsert:true)
diff --git a/jstests/core/write/update/upsert_and.js b/jstests/core/write/update/upsert_and.js
index 1e45cbe8dc2..c2bab3ab25c 100644
--- a/jstests/core/write/update/upsert_and.js
+++ b/jstests/core/write/update/upsert_and.js
@@ -5,7 +5,7 @@
 
 // tests to ensure fields in $and conditions are created when using the query to do upsert
 var res;
-coll = db.upsert4;
+let coll = db.upsert4;
 coll.drop();
 
 res = coll.update({_id: 1, $and: [{c: 1}, {d: 1}], a: 12}, {$inc: {y: 1}}, true);
diff --git a/jstests/core/write/update/upsert_fields.js b/jstests/core/write/update/upsert_fields.js
index 310bace4907..0433b15048b 100644
--- a/jstests/core/write/update/upsert_fields.js
+++ b/jstests/core/write/update/upsert_fields.js
@@ -12,7 +12,7 @@ coll.drop();
 
 var upsertedResult = function(query, expr) {
     coll.drop();
-    result = coll.update(query, expr, {upsert: true});
+    let result = coll.update(query, expr, {upsert: true});
     return result;
 };
 
diff --git a/jstests/core/write/update/upsert_shell.js b/jstests/core/write/update/upsert_shell.js
index 3ab07b50c21..252a0f4139a 100644
--- a/jstests/core/write/update/upsert_shell.js
+++ b/jstests/core/write/update/upsert_shell.js
@@ -5,7 +5,7 @@
 
 // tests to make sure that the new _id is returned after the insert in the shell
 var l;
-t = db.upsert1;
+let t = db.upsert1;
 t.drop();
 
 // make sure the new _id is returned when $mods are used
diff --git a/jstests/core/write/validate_user_documents.js b/jstests/core/write/validate_user_documents.js
index 2a30ed0fea8..65aa7cde07e 100644
--- a/jstests/core/write/validate_user_documents.js
+++ b/jstests/core/write/validate_user_documents.js
@@ -10,7 +10,7 @@
 // Ensure that inserts and updates of the system.users collection validate the schema of inserted
 // documents.
 
-mydb = db.getSiblingDB("validate_user_documents");
+let mydb = db.getSiblingDB("validate_user_documents");
 
 function assertGLEOK(status) {
     assert(status.ok && status.err === null, "Expected OK status object; found " + tojson(status));
author	Matt Broadstone <mbroadst@mongodb.com>	2023-05-07 16:15:25 +0000
committer	Evergreen Agent <no-reply@evergreen.mongodb.com>	2023-05-07 16:55:23 +0000
commit	43b87324302209cbfa240d6c6b520007669e4ea6 (patch)
tree	7039a07f7116ad86df64fd21eee62f84053ba92e /jstests/core
parent	948bf37c910d9911160e3b275d3c51b146a9c923 (diff)
download	mongo-43b87324302209cbfa240d6c6b520007669e4ea6.tar.gz