esm: phase two of new esm implementation

This PR updates the current `--experimental-modules` implementation
based on the work of the modules team  and reflects Phase 2 of our
new modules plan.

The largest differences from the current implementation include

* `packge.type` which can be either `module` or `commonjs`
  - `type: "commonjs"`:
    - `.js` is parsed as commonjs
    - default for entry point without an extension is commonjs
  - `type: "module"`:
    - `.js` is parsed as esm
    - does not support loading JSON or Native Module by default
    - default for entry point without an extension is esm
* `--entry-type=[mode]`
  - allows you set the type on entry point.
* A new file extension `.cjs`.
  - this is specifically to support importing commonjs in the
    `module` mode.
  - this is only in the esm loader, the commonjs loader remains
    untouched, but the extension will work in the old loader if you use
    the full file path.
* `--es-module-specifier-resolution=[type]`
  - options are `explicit` (default) and `node`
  - by default our loader will not allow for optional extensions in
    the import, the path for a module must include the extension if
    there is one
  - by default our loader will not allow for importing directories that
    have an index file
  - developers can use `--es-module-specifier-resolution=node` to
    enable the commonjs specifier resolution algorithm
  - This is not a “feature” but rather an implementation for
    experimentation. It is expected to change before the flag is
    removed
* `--experimental-json-loader`
  - the only way to import json when `"type": "module"`
  - when enable all `import 'thing.json'` will go through the
    experimental loader independent of mode
  - based on https://github.com/whatwg/html/issues/4315
* You can use `package.main` to set an entry point for a module
  - the file extensions used in main will be resolved based on the
    `type` of the module

Refs: https://github.com/nodejs/modules/blob/master/doc/plan-for-new-modules-implementation.md
Refs: https://github.com/GeoffreyBooth/node-import-file-specifier-resolution-proposal
Refs: https://github.com/nodejs/modules/pull/180
Refs: https://github.com/nodejs/ecmascript-modules/pull/6
Refs: https://github.com/nodejs/ecmascript-modules/pull/12
Refs: https://github.com/nodejs/ecmascript-modules/pull/28
Refs: https://github.com/nodejs/modules/issues/255
Refs: https://github.com/whatwg/html/issues/4315
Refs: https://github.com/w3c/webcomponents/issues/770
Co-authored-by: Myles Borins <MylesBorins@google.com>
Co-authored-by: John-David Dalton <john.david.dalton@gmail.com>
Co-authored-by: Evan Plaice <evanplaice@gmail.com>
Co-authored-by: Geoffrey Booth <webmaster@geoffreybooth.com>
Co-authored-by: Michaël Zasso <targos@protonmail.com>

PR-URL: https://github.com/nodejs/node/pull/26745
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Guy Bedford <guybedford@gmail.com>
Reviewed-By: Ben Coe <bencoe@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>

100 files changed, 580 insertions, 145 deletions

diff --git a/test/addons/hello-world-esm/binding.cc b/test/addons/hello-world-esm/binding.cc
deleted file mode 100644
index 02eecec099..0000000000
--- a/test/addons/hello-world-esm/binding.cc
+++ /dev/null
@@ -1,14 +0,0 @@
-#include <node.h>
-#include <v8.h>
-
-void Method(const v8::FunctionCallbackInfo<v8::Value>& args) {
-  v8::Isolate* isolate = args.GetIsolate();
-  args.GetReturnValue().Set(v8::String::NewFromUtf8(
-        isolate, "world", v8::NewStringType::kNormal).ToLocalChecked());
-}
-
-void init(v8::Local<v8::Object> exports) {
-  NODE_SET_METHOD(exports, "hello", Method);
-}
-
-NODE_MODULE(NODE_GYP_MODULE_NAME, init)
diff --git a/test/addons/hello-world-esm/binding.gyp b/test/addons/hello-world-esm/binding.gyp
deleted file mode 100644
index 55fbe7050f..0000000000
--- a/test/addons/hello-world-esm/binding.gyp
+++ /dev/null
@@ -1,9 +0,0 @@
-{
-  'targets': [
-    {
-      'target_name': 'binding',
-      'sources': [ 'binding.cc' ],
-      'includes': ['../common.gypi'],
-    }
-  ]
-}
diff --git a/test/addons/hello-world-esm/test.js b/test/addons/hello-world-esm/test.js
deleted file mode 100644
index d0faf65540..0000000000
--- a/test/addons/hello-world-esm/test.js
+++ /dev/null
@@ -1,20 +0,0 @@
-'use strict';
-const common = require('../../common');
-
-const assert = require('assert');
-const { spawnSync } = require('child_process');
-const { copyFileSync } = require('fs');
-const { join } = require('path');
-
-const buildDir = join(__dirname, 'build');
-
-copyFileSync(join(buildDir, common.buildType, 'binding.node'),
-             join(buildDir, 'binding.node'));
-
-const result = spawnSync(process.execPath,
-                         ['--experimental-modules', `${__dirname}/test.mjs`]);
-
-assert.ifError(result.error);
-// TODO: Uncomment this once ESM is no longer experimental.
-// assert.strictEqual(result.stderr.toString().trim(), '');
-assert.strictEqual(result.stdout.toString().trim(), 'binding.hello() = world');
diff --git a/test/addons/hello-world-esm/test.mjs b/test/addons/hello-world-esm/test.mjs
deleted file mode 100644
index d98de5bf87..0000000000
--- a/test/addons/hello-world-esm/test.mjs
+++ /dev/null
@@ -1,6 +0,0 @@
-/* eslint-disable node-core/required-modules */
-
-import assert from 'assert';
-import binding from './build/binding.node';
-assert.strictEqual(binding.hello(), 'world');
-console.log('binding.hello() =', binding.hello());
diff --git a/test/common/index.mjs b/test/common/index.mjs
index de9119f37e..41592098eb 100644
--- a/test/common/index.mjs
+++ b/test/common/index.mjs
@@ -1,6 +1,15 @@
 // Flags: --experimental-modules
 /* eslint-disable node-core/required-modules */
-import common from './index.js';
+
+import { createRequireFromPath } from 'module';
+import { fileURLToPath as toPath } from 'url';
+
+function createRequire(metaUrl) {
+  return createRequireFromPath(toPath(metaUrl));
+}
+
+const require = createRequire(import.meta.url);
+const common = require('./index.js');
 
 const {
   isMainThread,
@@ -91,5 +100,6 @@ export {
   getBufferSources,
   disableCrashOnUnhandledRejection,
   getTTYfd,
-  runWithInvalidFD
+  runWithInvalidFD,
+  createRequire
 };
diff --git a/test/es-module/test-esm-basic-imports.mjs b/test/es-module/test-esm-basic-imports.mjs
index 78a4106f94..d9bb22be0a 100644
--- a/test/es-module/test-esm-basic-imports.mjs
+++ b/test/es-module/test-esm-basic-imports.mjs
@@ -1,5 +1,6 @@
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
+import '../common/index.mjs';
 import assert from 'assert';
 import ok from '../fixtures/es-modules/test-esm-ok.mjs';
 import okShebang from './test-esm-shebang.mjs';
diff --git a/test/es-module/test-esm-cyclic-dynamic-import.mjs b/test/es-module/test-esm-cyclic-dynamic-import.mjs
index c8dfff919c..a207efc73e 100644
--- a/test/es-module/test-esm-cyclic-dynamic-import.mjs
+++ b/test/es-module/test-esm-cyclic-dynamic-import.mjs
@@ -1,3 +1,4 @@
 // Flags: --experimental-modules
-import '../common';
-import('./test-esm-cyclic-dynamic-import');
+/* eslint-disable node-core/required-modules */
+import '../common/index.mjs';
+import('./test-esm-cyclic-dynamic-import.mjs');
diff --git a/test/es-module/test-esm-double-encoding.mjs b/test/es-module/test-esm-double-encoding.mjs
index c81d0530d3..9366d4bd6b 100644
--- a/test/es-module/test-esm-double-encoding.mjs
+++ b/test/es-module/test-esm-double-encoding.mjs
@@ -1,6 +1,7 @@
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
+import '../common/index.mjs';
 
 // Assert we can import files with `%` in their pathname.
 
-import '../fixtures/es-modules/test-esm-double-encoding-native%2520.js';
+import '../fixtures/es-modules/test-esm-double-encoding-native%2520.mjs';
diff --git a/test/es-module/test-esm-dynamic-import.js b/test/es-module/test-esm-dynamic-import.js
index b271d43c80..ca9c99007b 100644
--- a/test/es-module/test-esm-dynamic-import.js
+++ b/test/es-module/test-esm-dynamic-import.js
@@ -1,4 +1,5 @@
 // Flags: --experimental-modules
+
 'use strict';
 const common = require('../common');
 const assert = require('assert');
@@ -17,7 +18,7 @@ function expectErrorProperty(result, propertyKey, value) {
 }
 
 function expectMissingModuleError(result) {
-  expectErrorProperty(result, 'code', 'MODULE_NOT_FOUND');
+  expectErrorProperty(result, 'code', 'ERR_MODULE_NOT_FOUND');
 }
 
 function expectOkNamespace(result) {
diff --git a/test/es-module/test-esm-encoded-path.mjs b/test/es-module/test-esm-encoded-path.mjs
index 365a425afa..2cabfdacff 100644
--- a/test/es-module/test-esm-encoded-path.mjs
+++ b/test/es-module/test-esm-encoded-path.mjs
@@ -1,5 +1,6 @@
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
+import '../common/index.mjs';
 import assert from 'assert';
 // ./test-esm-ok.mjs
 import ok from '../fixtures/es-modules/test-%65%73%6d-ok.mjs';
diff --git a/test/es-module/test-esm-error-cache.js b/test/es-module/test-esm-error-cache.js
index 98244615ef..79f76357ec 100644
--- a/test/es-module/test-esm-error-cache.js
+++ b/test/es-module/test-esm-error-cache.js
@@ -1,11 +1,11 @@
-'use strict';
-
 // Flags: --experimental-modules
 
+'use strict';
+
 require('../common');
 const assert = require('assert');
 
-const file = '../fixtures/syntax/bad_syntax.js';
+const file = '../fixtures/syntax/bad_syntax.mjs';
 
 let error;
 (async () => {
diff --git a/test/es-module/test-esm-forbidden-globals.mjs b/test/es-module/test-esm-forbidden-globals.mjs
index 4e777412a3..cf110ff290 100644
--- a/test/es-module/test-esm-forbidden-globals.mjs
+++ b/test/es-module/test-esm-forbidden-globals.mjs
@@ -1,5 +1,6 @@
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
+import '../common/index.mjs';
 
 // eslint-disable-next-line no-undef
 if (typeof arguments !== 'undefined') {
diff --git a/test/es-module/test-esm-import-meta.mjs b/test/es-module/test-esm-import-meta.mjs
index c17e0e20d4..4c34b337fb 100644
--- a/test/es-module/test-esm-import-meta.mjs
+++ b/test/es-module/test-esm-import-meta.mjs
@@ -1,6 +1,7 @@
 // Flags: --experimental-modules
+/* eslint-disable node-core/required-modules */
 
-import '../common';
+import '../common/index.mjs';
 import assert from 'assert';
 
 assert.strictEqual(Object.getPrototypeOf(import.meta), null);
diff --git a/test/es-module/test-esm-json-cache.mjs b/test/es-module/test-esm-json-cache.mjs
new file mode 100644
index 0000000000..ecd27c5488
--- /dev/null
+++ b/test/es-module/test-esm-json-cache.mjs
@@ -0,0 +1,26 @@
+// Flags: --experimental-modules --experimental-json-modules
+/* eslint-disable node-core/required-modules */
+import '../common/index.mjs';
+
+import { strictEqual, deepStrictEqual } from 'assert';
+
+import { createRequireFromPath as createRequire } from 'module';
+import { fileURLToPath as fromURL } from 'url';
+
+import mod from '../fixtures/es-modules/json-cache/mod.cjs';
+import another from '../fixtures/es-modules/json-cache/another.cjs';
+import test from '../fixtures/es-modules/json-cache/test.json';
+
+const require = createRequire(fromURL(import.meta.url));
+
+const modCjs = require('../fixtures/es-modules/json-cache/mod.cjs');
+const anotherCjs = require('../fixtures/es-modules/json-cache/another.cjs');
+const testCjs = require('../fixtures/es-modules/json-cache/test.json');
+
+strictEqual(mod.one, 1);
+strictEqual(another.one, 'zalgo');
+strictEqual(test.one, 'it comes');
+
+deepStrictEqual(mod, modCjs);
+deepStrictEqual(another, anotherCjs);
+deepStrictEqual(test, testCjs);
diff --git a/test/es-module/test-esm-json.mjs b/test/es-module/test-esm-json.mjs
index a7146d19a9..b140d031ca 100644
--- a/test/es-module/test-esm-json.mjs
+++ b/test/es-module/test-esm-json.mjs
@@ -1,8 +1,9 @@
-// Flags: --experimental-modules
-import '../common';
-import assert from 'assert';
-import ok from '../fixtures/es-modules/test-esm-ok.mjs';
-import json from '../fixtures/es-modules/json.json';
+// Flags: --experimental-modules --experimental-json-modules
+/* eslint-disable node-core/required-modules */
 
-assert(ok);
-assert.strictEqual(json.val, 42);
+import '../common/index.mjs';
+import { strictEqual } from 'assert';
+
+import secret from '../fixtures/experimental.json';
+
+strictEqual(secret.ofLife, 42);
diff --git a/test/es-module/test-esm-live-binding.mjs b/test/es-module/test-esm-live-binding.mjs
index d151e004df..880a6c389b 100644
--- a/test/es-module/test-esm-live-binding.mjs
+++ b/test/es-module/test-esm-live-binding.mjs
@@ -1,6 +1,7 @@
 // Flags: --experimental-modules
+/* eslint-disable node-core/required-modules */
 
-import '../common';
+import '../common/index.mjs';
 import assert from 'assert';
 
 import fs, { readFile, readFileSync } from 'fs';
diff --git a/test/es-module/test-esm-loader-invalid-format.mjs b/test/es-module/test-esm-loader-invalid-format.mjs
index f8714d4aa1..c3f3a87407 100644
--- a/test/es-module/test-esm-loader-invalid-format.mjs
+++ b/test/es-module/test-esm-loader-invalid-format.mjs
@@ -1,5 +1,6 @@
 // Flags: --experimental-modules --loader ./test/fixtures/es-module-loaders/loader-invalid-format.mjs
-import { expectsError, mustCall } from '../common';
+/* eslint-disable node-core/required-modules */
+import { expectsError, mustCall } from '../common/index.mjs';
 import assert from 'assert';
 
 import('../fixtures/es-modules/test-esm-ok.mjs')
diff --git a/test/es-module/test-esm-loader-invalid-url.mjs b/test/es-module/test-esm-loader-invalid-url.mjs
index 43971a2e6e..9cf17b2478 100644
--- a/test/es-module/test-esm-loader-invalid-url.mjs
+++ b/test/es-module/test-esm-loader-invalid-url.mjs
@@ -1,5 +1,7 @@
 // Flags: --experimental-modules --loader ./test/fixtures/es-module-loaders/loader-invalid-url.mjs
-import { expectsError, mustCall } from '../common';
+/* eslint-disable node-core/required-modules */
+
+import { expectsError, mustCall } from '../common/index.mjs';
 import assert from 'assert';
 
 import('../fixtures/es-modules/test-esm-ok.mjs')
diff --git a/test/es-module/test-esm-loader-missing-dynamic-instantiate-hook.mjs b/test/es-module/test-esm-loader-missing-dynamic-instantiate-hook.mjs
index f2b37f7e8a..ab2da7adce 100644
--- a/test/es-module/test-esm-loader-missing-dynamic-instantiate-hook.mjs
+++ b/test/es-module/test-esm-loader-missing-dynamic-instantiate-hook.mjs
@@ -1,6 +1,7 @@
 // Flags: --experimental-modules --loader ./test/fixtures/es-module-loaders/missing-dynamic-instantiate-hook.mjs
+/* eslint-disable node-core/required-modules */
 
-import { expectsError } from '../common';
+import { expectsError } from '../common/index.mjs';
 
 import('test').catch(expectsError({
   code: 'ERR_MISSING_DYNAMIC_INSTANTIATE_HOOK',
diff --git a/test/es-module/test-esm-loader-modulemap.js b/test/es-module/test-esm-loader-modulemap.js
index 946d54ffaa..5493c6c47c 100644
--- a/test/es-module/test-esm-loader-modulemap.js
+++ b/test/es-module/test-esm-loader-modulemap.js
@@ -7,7 +7,7 @@
 const common = require('../common');
 
 const { URL } = require('url');
-const Loader = require('internal/modules/esm/loader');
+const { Loader } = require('internal/modules/esm/loader');
 const ModuleMap = require('internal/modules/esm/module_map');
 const ModuleJob = require('internal/modules/esm/module_job');
 const createDynamicModule = require(
diff --git a/test/es-module/test-esm-loader-search.js b/test/es-module/test-esm-loader-search.js
index 0ca8990cb7..b5e0d8d656 100644
--- a/test/es-module/test-esm-loader-search.js
+++ b/test/es-module/test-esm-loader-search.js
@@ -5,13 +5,13 @@
 
 const common = require('../common');
 
-const { search } = require('internal/modules/esm/default_resolve');
+const resolve = require('internal/modules/esm/default_resolve');
 
 common.expectsError(
-  () => search('target', undefined),
+  () => resolve('target', undefined),
   {
-    code: 'ERR_MISSING_MODULE',
+    code: 'ERR_MODULE_NOT_FOUND',
     type: Error,
-    message: 'Cannot find module target'
+    message: /Cannot find package 'target'/
   }
 );
diff --git a/test/es-module/test-esm-main-lookup.mjs b/test/es-module/test-esm-main-lookup.mjs
index ca313a1d26..19c025beab 100644
--- a/test/es-module/test-esm-main-lookup.mjs
+++ b/test/es-module/test-esm-main-lookup.mjs
@@ -1,6 +1,26 @@
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
+import '../common/index.mjs';
 import assert from 'assert';
-import main from '../fixtures/es-modules/pjson-main';
 
-assert.strictEqual(main, 'main');
+async function main() {
+  let mod;
+  try {
+    mod = await import('../fixtures/es-modules/pjson-main');
+  } catch (e) {
+    assert.strictEqual(e.code, 'ERR_MODULE_NOT_FOUND');
+  }
+
+  assert.strictEqual(mod, undefined);
+
+  try {
+    mod = await import('../fixtures/es-modules/pjson-main/main.mjs');
+  } catch (e) {
+    console.log(e);
+    assert.fail();
+  }
+
+  assert.strictEqual(mod.main, 'main');
+}
+
+main();
diff --git a/test/es-module/test-esm-named-exports.mjs b/test/es-module/test-esm-named-exports.mjs
index 3aae9230de..e235f598cb 100644
--- a/test/es-module/test-esm-named-exports.mjs
+++ b/test/es-module/test-esm-named-exports.mjs
@@ -1,5 +1,6 @@
 // Flags: --experimental-modules --loader ./test/fixtures/es-module-loaders/builtin-named-exports-loader.mjs
-import '../common';
+/* eslint-disable node-core/required-modules */
+import '../common/index.mjs';
 import { readFile } from 'fs';
 import assert from 'assert';
 import ok from '../fixtures/es-modules/test-esm-ok.mjs';
diff --git a/test/es-module/test-esm-namespace.mjs b/test/es-module/test-esm-namespace.mjs
index da1286d0f4..38b7ef12d5 100644
--- a/test/es-module/test-esm-namespace.mjs
+++ b/test/es-module/test-esm-namespace.mjs
@@ -1,5 +1,7 @@
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
+
+import '../common/index.mjs';
 import * as fs from 'fs';
 import assert from 'assert';
 import Module from 'module';
diff --git a/test/es-module/test-esm-no-extension.js b/test/es-module/test-esm-no-extension.js
new file mode 100644
index 0000000000..3e9ffb2bbc
--- /dev/null
+++ b/test/es-module/test-esm-no-extension.js
@@ -0,0 +1,35 @@
+'use strict';
+
+const common = require('../common');
+const fixtures = require('../common/fixtures');
+const { spawn } = require('child_process');
+const assert = require('assert');
+
+const entry = fixtures.path('/es-modules/noext-esm');
+
+// Run a module that does not have extension
+// This is to ensure the --entry-type works as expected
+
+const child = spawn(process.execPath, [
+  '--experimental-modules',
+  '--entry-type=module',
+  entry
+]);
+
+let stderr = '';
+child.stderr.setEncoding('utf8');
+child.stderr.on('data', (data) => {
+  stderr += data;
+});
+let stdout = '';
+child.stdout.setEncoding('utf8');
+child.stdout.on('data', (data) => {
+  stdout += data;
+});
+child.on('close', common.mustCall((code, signal) => {
+  assert.strictEqual(code, 0);
+  assert.strictEqual(signal, null);
+  assert.strictEqual(stdout, 'executed\n');
+  assert.strictEqual(stderr, `(node:${child.pid}) ` +
+      'ExperimentalWarning: The ESM module loader is experimental.\n');
+}));
diff --git a/test/es-module/test-esm-preserve-symlinks-not-found.mjs b/test/es-module/test-esm-preserve-symlinks-not-found.mjs
index 5119957bae..b5be2d7e63 100644
--- a/test/es-module/test-esm-preserve-symlinks-not-found.mjs
+++ b/test/es-module/test-esm-preserve-symlinks-not-found.mjs
@@ -1,3 +1,3 @@
 // Flags: --experimental-modules --loader ./test/fixtures/es-module-loaders/not-found-assert-loader.mjs
 /* eslint-disable node-core/required-modules */
-import './not-found';
+import './not-found.mjs';
diff --git a/test/es-module/test-esm-process.mjs b/test/es-module/test-esm-process.mjs
index ea9b4b4936..3a23573d33 100644
--- a/test/es-module/test-esm-process.mjs
+++ b/test/es-module/test-esm-process.mjs
@@ -1,5 +1,6 @@
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
+import '../common/index.mjs';
 import assert from 'assert';
 import process from 'process';
 
diff --git a/test/es-module/test-esm-require-cache.mjs b/test/es-module/test-esm-require-cache.mjs
index ff32cde36f..09030e0578 100644
--- a/test/es-module/test-esm-require-cache.mjs
+++ b/test/es-module/test-esm-require-cache.mjs
@@ -1,7 +1,12 @@
 // Flags: --experimental-modules
-import '../common';
-import '../fixtures/es-module-require-cache/preload.js';
-import '../fixtures/es-module-require-cache/counter.js';
+/* eslint-disable node-core/required-modules */
+import { createRequire } from '../common/index.mjs';
 import assert from 'assert';
+//
+const require = createRequire(import.meta.url);
+
+require('../fixtures/es-module-require-cache/preload.js');
+require('../fixtures/es-module-require-cache/counter.js');
+
 assert.strictEqual(global.counter, 1);
 delete global.counter;
diff --git a/test/es-module/test-esm-shared-loader-dep.mjs b/test/es-module/test-esm-shared-loader-dep.mjs
index 5c274d835c..b8953ab1ec 100644
--- a/test/es-module/test-esm-shared-loader-dep.mjs
+++ b/test/es-module/test-esm-shared-loader-dep.mjs
@@ -1,7 +1,11 @@
 // Flags: --experimental-modules --loader ./test/fixtures/es-module-loaders/loader-shared-dep.mjs
-import '../common';
+/* eslint-disable node-core/required-modules */
+import { createRequire } from '../common/index.mjs';
+
 import assert from 'assert';
 import '../fixtures/es-modules/test-esm-ok.mjs';
-import dep from '../fixtures/es-module-loaders/loader-dep.js';
 
-assert.strictEqual(dep.format, 'esm');
+const require = createRequire(import.meta.url);
+const dep = require('../fixtures/es-module-loaders/loader-dep.js');
+
+assert.strictEqual(dep.format, 'module');
diff --git a/test/es-module/test-esm-shebang.mjs b/test/es-module/test-esm-shebang.mjs
index d5faace479..486e04dade 100644
--- a/test/es-module/test-esm-shebang.mjs
+++ b/test/es-module/test-esm-shebang.mjs
@@ -1,6 +1,7 @@
 #! }]) // isn't js
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
+import '../common/index.mjs';
 
 const isJs = true;
 export default isJs;
diff --git a/test/es-module/test-esm-snapshot.mjs b/test/es-module/test-esm-snapshot.mjs
index 3d4b44bbdd..3997e24ed7 100644
--- a/test/es-module/test-esm-snapshot.mjs
+++ b/test/es-module/test-esm-snapshot.mjs
@@ -1,7 +1,8 @@
 // Flags: --experimental-modules
-import '../common';
-import '../fixtures/es-modules/esm-snapshot-mutator';
-import one from '../fixtures/es-modules/esm-snapshot';
+/* eslint-disable node-core/required-modules */
+import '../common/index.mjs';
+import '../fixtures/es-modules/esm-snapshot-mutator.js';
+import one from '../fixtures/es-modules/esm-snapshot.js';
 import assert from 'assert';
 
 assert.strictEqual(one, 1);
diff --git a/test/es-module/test-esm-specifiers.mjs b/test/es-module/test-esm-specifiers.mjs
new file mode 100644
index 0000000000..0c5e1ac04a
--- /dev/null
+++ b/test/es-module/test-esm-specifiers.mjs
@@ -0,0 +1,35 @@
+// Flags: --experimental-modules --es-module-specifier-resolution=node
+import { mustNotCall } from '../common';
+import assert from 'assert';
+
+// commonJS index.js
+import commonjs from '../fixtures/es-module-specifiers/package-type-commonjs';
+// esm index.js
+import module from '../fixtures/es-module-specifiers/package-type-module';
+// Notice the trailing slash
+import success, { explicit, implicit, implicitModule, getImplicitCommonjs }
+  from '../fixtures/es-module-specifiers/';
+
+assert.strictEqual(commonjs, 'commonjs');
+assert.strictEqual(module, 'module');
+assert.strictEqual(success, 'success');
+assert.strictEqual(explicit, 'esm');
+assert.strictEqual(implicit, 'esm');
+assert.strictEqual(implicitModule, 'esm');
+
+async function main() {
+  try {
+    await import('../fixtures/es-module-specifiers/do-not-exist.js');
+  } catch (e) {
+    // Files that do not exist should throw
+    assert.strictEqual(e.name, 'Error');
+  }
+  try {
+    await getImplicitCommonjs();
+  } catch (e) {
+    // Legacy loader cannot resolve .mjs automatically from main
+    assert.strictEqual(e.name, 'Error');
+  }
+}
+
+main().catch(mustNotCall);
diff --git a/test/es-module/test-esm-symlink-main.js b/test/es-module/test-esm-symlink-main.js
index f7631ef2e5..871180f5cc 100644
--- a/test/es-module/test-esm-symlink-main.js
+++ b/test/es-module/test-esm-symlink-main.js
@@ -9,7 +9,7 @@ const fs = require('fs');
 tmpdir.refresh();
 
 const realPath = path.resolve(__dirname, '../fixtures/es-modules/symlink.mjs');
-const symlinkPath = path.resolve(tmpdir.path, 'symlink.js');
+const symlinkPath = path.resolve(tmpdir.path, 'symlink.mjs');
 
 try {
   fs.symlinkSync(realPath, symlinkPath);
diff --git a/test/es-module/test-esm-symlink-type.js b/test/es-module/test-esm-symlink-type.js
new file mode 100644
index 0000000000..6159ebecd1
--- /dev/null
+++ b/test/es-module/test-esm-symlink-type.js
@@ -0,0 +1,77 @@
+'use strict';
+const common = require('../common');
+const fixtures = require('../common/fixtures');
+const path = require('path');
+const assert = require('assert');
+const exec = require('child_process').execFile;
+const fs = require('fs');
+
+const tmpdir = require('../common/tmpdir');
+tmpdir.refresh();
+const tmpDir = tmpdir.path;
+
+// Check that running the symlink executes the target as the correct type
+const symlinks = [
+  {
+    source: 'extensionless-symlink-to-mjs-file',
+    target: fixtures.path('es-modules/mjs-file.mjs'),
+    prints: '.mjs file',
+    errorsWithPreserveSymlinksMain: false
+  }, {
+    source: 'extensionless-symlink-to-cjs-file',
+    target: fixtures.path('es-modules/cjs-file.cjs'),
+    prints: '.cjs file',
+    errorsWithPreserveSymlinksMain: false
+  }, {
+    source: 'extensionless-symlink-to-file-in-module-scope',
+    target: fixtures.path('es-modules/package-type-module/index.js'),
+    prints: 'package-type-module',
+    // The package scope of the symlinks' sources is commonjs, and this
+    // symlink's target is a .js file in a module scope, so when the scope
+    // is evaluated based on the source (commonjs) this esm file should error
+    errorsWithPreserveSymlinksMain: true
+  }, {
+    source: 'extensionless-symlink-to-file-in-explicit-commonjs-scope',
+    target: fixtures.path('es-modules/package-type-commonjs/index.js'),
+    prints: 'package-type-commonjs',
+    errorsWithPreserveSymlinksMain: false
+  }, {
+    source: 'extensionless-symlink-to-file-in-implicit-commonjs-scope',
+    target: fixtures.path('es-modules/package-without-type/index.js'),
+    prints: 'package-without-type',
+    errorsWithPreserveSymlinksMain: false
+  }
+];
+
+symlinks.forEach((symlink) => {
+  const mainPath = path.join(tmpDir, symlink.source);
+  fs.symlinkSync(symlink.target, mainPath);
+
+  const flags = [
+    '--experimental-modules',
+    '--experimental-modules --preserve-symlinks-main'
+  ];
+  flags.forEach((nodeOptions) => {
+    const opts = {
+      env: Object.assign({}, process.env, { NODE_OPTIONS: nodeOptions })
+    };
+    exec(process.execPath, [mainPath], opts, common.mustCall(
+      (err, stdout) => {
+        if (nodeOptions.includes('--preserve-symlinks-main')) {
+          if (symlink.errorsWithPreserveSymlinksMain &&
+              err.toString().includes('Error')) return;
+          else if (!symlink.errorsWithPreserveSymlinksMain &&
+                    stdout.includes(symlink.prints)) return;
+          assert.fail(`For ${JSON.stringify(symlink)}, ${
+            (symlink.errorsWithPreserveSymlinksMain) ?
+              'failed to error' : 'errored unexpectedly'
+          } with --preserve-symlinks-main`);
+        } else {
+          if (stdout.includes(symlink.prints)) return;
+          assert.fail(`For ${JSON.stringify(symlink)}, failed to find ` +
+            `${symlink.prints} in: <\n${stdout}\n>`);
+        }
+      }
+    ));
+  });
+});
diff --git a/test/es-module/test-esm-symlink.js b/test/es-module/test-esm-symlink.js
index 232925a52e..9b9eb98cd9 100644
--- a/test/es-module/test-esm-symlink.js
+++ b/test/es-module/test-esm-symlink.js
@@ -12,8 +12,8 @@ const tmpDir = tmpdir.path;
 
 const entry = path.join(tmpDir, 'entry.mjs');
 const real = path.join(tmpDir, 'index.mjs');
-const link_absolute_path = path.join(tmpDir, 'absolute');
-const link_relative_path = path.join(tmpDir, 'relative');
+const link_absolute_path = path.join(tmpDir, 'absolute.mjs');
+const link_relative_path = path.join(tmpDir, 'relative.mjs');
 const link_ignore_extension = path.join(tmpDir,
                                         'ignore_extension.json');
 const link_directory = path.join(tmpDir, 'directory');
@@ -22,15 +22,13 @@ fs.writeFileSync(real, 'export default [];');
 fs.writeFileSync(entry, `
 import assert from 'assert';
 import real from './index.mjs';
-import absolute from './absolute';
-import relative from './relative';
+import absolute from './absolute.mjs';
+import relative from './relative.mjs';
 import ignoreExtension from './ignore_extension.json';
-import directory from './directory';
 
 assert.strictEqual(absolute, real);
 assert.strictEqual(relative, real);
 assert.strictEqual(ignoreExtension, real);
-assert.strictEqual(directory, real);
 `);
 
 try {
diff --git a/test/es-module/test-esm-throw-undefined.mjs b/test/es-module/test-esm-throw-undefined.mjs
index 541127eee5..97e917da5e 100644
--- a/test/es-module/test-esm-throw-undefined.mjs
+++ b/test/es-module/test-esm-throw-undefined.mjs
@@ -1,11 +1,13 @@
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
+
+import '../common/index.mjs';
 import assert from 'assert';
 
 async function doTest() {
   await assert.rejects(
     async () => {
-      await import('../fixtures/es-module-loaders/throw-undefined');
+      await import('../fixtures/es-module-loaders/throw-undefined.mjs');
     },
     (e) => e === undefined
   );
diff --git a/test/es-module/test-esm-type-flag-errors.js b/test/es-module/test-esm-type-flag-errors.js
new file mode 100644
index 0000000000..612ada584d
--- /dev/null
+++ b/test/es-module/test-esm-type-flag-errors.js
@@ -0,0 +1,53 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const exec = require('child_process').execFile;
+
+const mjsFile = require.resolve('../fixtures/es-modules/mjs-file.mjs');
+const cjsFile = require.resolve('../fixtures/es-modules/cjs-file.cjs');
+const packageWithoutTypeMain =
+  require.resolve('../fixtures/es-modules/package-without-type/index.js');
+const packageTypeCommonJsMain =
+  require.resolve('../fixtures/es-modules/package-type-commonjs/index.js');
+const packageTypeModuleMain =
+  require.resolve('../fixtures/es-modules/package-type-module/index.js');
+
+// Check that running `node` without options works
+expect('', mjsFile, '.mjs file');
+expect('', cjsFile, '.cjs file');
+expect('', packageTypeModuleMain, 'package-type-module');
+expect('', packageTypeCommonJsMain, 'package-type-commonjs');
+expect('', packageWithoutTypeMain, 'package-without-type');
+
+// Check that running with --entry-type and no package.json "type" works
+expect('--entry-type=commonjs', packageWithoutTypeMain, 'package-without-type');
+expect('--entry-type=module', packageWithoutTypeMain, 'package-without-type');
+
+// Check that running with conflicting --entry-type flags throws errors
+expect('--entry-type=commonjs', mjsFile, 'ERR_ENTRY_TYPE_MISMATCH', true);
+expect('--entry-type=module', cjsFile, 'ERR_ENTRY_TYPE_MISMATCH', true);
+expect('--entry-type=commonjs', packageTypeModuleMain,
+       'ERR_ENTRY_TYPE_MISMATCH', true);
+expect('--entry-type=module', packageTypeCommonJsMain,
+       'ERR_ENTRY_TYPE_MISMATCH', true);
+
+function expect(opt = '', inputFile, want, wantsError = false) {
+  // TODO: Remove when --experimental-modules is unflagged
+  opt = `--experimental-modules ${opt}`;
+  const argv = [inputFile];
+  const opts = {
+    env: Object.assign({}, process.env, { NODE_OPTIONS: opt }),
+    maxBuffer: 1e6,
+  };
+  exec(process.execPath, argv, opts, common.mustCall((err, stdout, stderr) => {
+    if (wantsError) {
+      stdout = stderr;
+    } else {
+      assert.ifError(err);
+    }
+    if (stdout.includes(want)) return;
+
+    const o = JSON.stringify(opt);
+    assert.fail(`For ${o}, failed to find ${want} in: <\n${stdout}\n>`);
+  }));
+}
diff --git a/test/es-module/test-esm-type-flag.mjs b/test/es-module/test-esm-type-flag.mjs
new file mode 100644
index 0000000000..2f5d0b626a
--- /dev/null
+++ b/test/es-module/test-esm-type-flag.mjs
@@ -0,0 +1,11 @@
+// Flags: --experimental-modules --entry-type=module
+/* eslint-disable node-core/required-modules */
+import cjs from '../fixtures/baz.js';
+import '../common/index.mjs';
+import { message } from '../fixtures/es-modules/message.mjs';
+import assert from 'assert';
+
+// Assert we loaded esm dependency as ".js" in this mode
+assert.strictEqual(message, 'A message');
+// Assert we loaded CommonJS dependency
+assert.strictEqual(cjs, 'perhaps I work');
diff --git a/test/fixtures/es-module-loaders/example-loader.mjs b/test/fixtures/es-module-loaders/example-loader.mjs
index a7cf276d4a..d8e0ddcba3 100644
--- a/test/fixtures/es-module-loaders/example-loader.mjs
+++ b/test/fixtures/es-module-loaders/example-loader.mjs
@@ -29,6 +29,6 @@ export function resolve(specifier, parentModuleURL = baseURL /*, defaultResolve
   }
   return {
     url: resolved.href,
-    format: 'esm'
+    format: 'module'
   };
 }
diff --git a/test/fixtures/es-module-loaders/js-loader.mjs b/test/fixtures/es-module-loaders/js-loader.mjs
index 2ac959a464..4b8a0fc365 100644
--- a/test/fixtures/es-module-loaders/js-loader.mjs
+++ b/test/fixtures/es-module-loaders/js-loader.mjs
@@ -15,6 +15,6 @@ export function resolve (specifier, base = baseURL) {
   const url = new URL(specifier, base).href;
   return {
     url,
-    format: 'esm'
+    format: 'module'
   };
 }
diff --git a/test/fixtures/es-module-loaders/loader-dep.js b/test/fixtures/es-module-loaders/loader-dep.js
index cf821afec1..c8154ac5db 100644
--- a/test/fixtures/es-module-loaders/loader-dep.js
+++ b/test/fixtures/es-module-loaders/loader-dep.js
@@ -1 +1 @@
-exports.format = 'esm';
+exports.format = 'module';
diff --git a/test/fixtures/es-module-loaders/loader-invalid-url.mjs b/test/fixtures/es-module-loaders/loader-invalid-url.mjs
index 12efbb5021..f653155899 100644
--- a/test/fixtures/es-module-loaders/loader-invalid-url.mjs
+++ b/test/fixtures/es-module-loaders/loader-invalid-url.mjs
@@ -1,3 +1,4 @@
+/* eslint-disable node-core/required-modules */
 export async function resolve(specifier, parentModuleURL, defaultResolve) {
   if (parentModuleURL && specifier === '../fixtures/es-modules/test-esm-ok.mjs') {
     return {
diff --git a/test/fixtures/es-module-loaders/loader-shared-dep.mjs b/test/fixtures/es-module-loaders/loader-shared-dep.mjs
index 1a19e4c892..3acafcce1e 100644
--- a/test/fixtures/es-module-loaders/loader-shared-dep.mjs
+++ b/test/fixtures/es-module-loaders/loader-shared-dep.mjs
@@ -1,7 +1,11 @@
-import dep from './loader-dep.js';
 import assert from 'assert';
 
+import {createRequire} from '../../common/index.mjs';
+
+const require = createRequire(import.meta.url);
+const dep = require('./loader-dep.js');
+
 export function resolve(specifier, base, defaultResolve) {
-  assert.strictEqual(dep.format, 'esm');
+  assert.strictEqual(dep.format, 'module');
   return defaultResolve(specifier, base);
 }
diff --git a/test/fixtures/es-module-loaders/loader-with-dep.mjs b/test/fixtures/es-module-loaders/loader-with-dep.mjs
index 944e6e438c..5afd3b2e21 100644
--- a/test/fixtures/es-module-loaders/loader-with-dep.mjs
+++ b/test/fixtures/es-module-loaders/loader-with-dep.mjs
@@ -1,4 +1,8 @@
-import dep from './loader-dep.js';
+import {createRequire} from '../../common/index.mjs';
+
+const require = createRequire(import.meta.url);
+const dep = require('./loader-dep.js');
+
 export function resolve (specifier, base, defaultResolve) {
   return {
     url: defaultResolve(specifier, base).url,
diff --git a/test/fixtures/es-module-loaders/not-found-assert-loader.mjs b/test/fixtures/es-module-loaders/not-found-assert-loader.mjs
index d15f294fe6..d3eebcd47e 100644
--- a/test/fixtures/es-module-loaders/not-found-assert-loader.mjs
+++ b/test/fixtures/es-module-loaders/not-found-assert-loader.mjs
@@ -12,11 +12,11 @@ export async function resolve (specifier, base, defaultResolve) {
     await defaultResolve(specifier, base);
   }
   catch (e) {
-    assert.strictEqual(e.code, 'MODULE_NOT_FOUND');
+    assert.strictEqual(e.code, 'ERR_MODULE_NOT_FOUND');
     return {
       format: 'builtin',
       url: 'fs'
     };
   }
-  assert.fail(`Module resolution for ${specifier} should be throw MODULE_NOT_FOUND`);
+  assert.fail(`Module resolution for ${specifier} should be throw ERR_MODULE_NOT_FOUND`);
 }
diff --git a/test/fixtures/es-module-loaders/syntax-error-import.mjs b/test/fixtures/es-module-loaders/syntax-error-import.mjs
index 9cad68c7ce..3a6bc5effc 100644
--- a/test/fixtures/es-module-loaders/syntax-error-import.mjs
+++ b/test/fixtures/es-module-loaders/syntax-error-import.mjs
@@ -1 +1 @@
-import { foo, notfound } from './module-named-exports';
+import { foo, notfound } from './module-named-exports.mjs';
diff --git a/test/fixtures/es-module-loaders/throw-undefined.mjs b/test/fixtures/es-module-loaders/throw-undefined.mjs
index f062276767..0349ae112d 100644
--- a/test/fixtures/es-module-loaders/throw-undefined.mjs
+++ b/test/fixtures/es-module-loaders/throw-undefined.mjs
@@ -1,3 +1,4 @@
 'use strict';
+/* eslint-disable node-core/required-modules */
 
 throw undefined;
diff --git a/test/fixtures/es-module-specifiers/index.mjs b/test/fixtures/es-module-specifiers/index.mjs
new file mode 100644
index 0000000000..2be7048513
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/index.mjs
@@ -0,0 +1,10 @@
+import explicit from 'explicit-main';
+import implicit from 'implicit-main';
+import implicitModule from 'implicit-main-type-module';
+
+function getImplicitCommonjs () {
+  return import('implicit-main-type-commonjs');
+}
+
+export {explicit, implicit, implicitModule, getImplicitCommonjs};
+export default 'success';
diff --git a/test/fixtures/es-module-specifiers/node_modules/explicit-main/entry.mjs b/test/fixtures/es-module-specifiers/node_modules/explicit-main/entry.mjs
new file mode 100644
index 0000000000..914e3a97d5
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/node_modules/explicit-main/entry.mjs
@@ -0,0 +1 @@
+export default 'esm';
diff --git a/test/fixtures/es-module-specifiers/node_modules/explicit-main/package.json b/test/fixtures/es-module-specifiers/node_modules/explicit-main/package.json
new file mode 100644
index 0000000000..e9457582ac
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/node_modules/explicit-main/package.json
@@ -0,0 +1,3 @@
+{
+  "main": "entry.mjs"
+}
\ No newline at end of file
diff --git a/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-commonjs/entry.mjs b/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-commonjs/entry.mjs
new file mode 100644
index 0000000000..914e3a97d5
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-commonjs/entry.mjs
@@ -0,0 +1 @@
+export default 'esm';
diff --git a/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-commonjs/package.json b/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-commonjs/package.json
new file mode 100644
index 0000000000..9093a7cc14
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-commonjs/package.json
@@ -0,0 +1,4 @@
+{
+  "main": "entry",
+  "type": "commonjs"
+}
diff --git a/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-module/entry.js b/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-module/entry.js
new file mode 100644
index 0000000000..5d7af588fd
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-module/entry.js
@@ -0,0 +1 @@
+export default 'nope';
diff --git a/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-module/entry.mjs b/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-module/entry.mjs
new file mode 100644
index 0000000000..914e3a97d5
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-module/entry.mjs
@@ -0,0 +1 @@
+export default 'esm';
diff --git a/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-module/package.json b/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-module/package.json
new file mode 100644
index 0000000000..5710280bad
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-module/package.json
@@ -0,0 +1,4 @@
+{
+  "main": "entry",
+  "type": "module"
+}
diff --git a/test/fixtures/es-module-specifiers/node_modules/implicit-main/entry.js b/test/fixtures/es-module-specifiers/node_modules/implicit-main/entry.js
new file mode 100644
index 0000000000..b2825bd3c9
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/node_modules/implicit-main/entry.js
@@ -0,0 +1 @@
+module.exports = 'cjs';
diff --git a/test/fixtures/es-module-specifiers/node_modules/implicit-main/entry.mjs b/test/fixtures/es-module-specifiers/node_modules/implicit-main/entry.mjs
new file mode 100644
index 0000000000..914e3a97d5
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/node_modules/implicit-main/entry.mjs
@@ -0,0 +1 @@
+export default 'esm';
diff --git a/test/fixtures/es-module-specifiers/node_modules/implicit-main/package.json b/test/fixtures/es-module-specifiers/node_modules/implicit-main/package.json
new file mode 100644
index 0000000000..5c07cf41bb
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/node_modules/implicit-main/package.json
@@ -0,0 +1,3 @@
+{
+  "main": "entry"
+}
diff --git a/test/fixtures/es-module-specifiers/package-type-commonjs/a.js b/test/fixtures/es-module-specifiers/package-type-commonjs/a.js
new file mode 100644
index 0000000000..2e7700bc63
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/package-type-commonjs/a.js
@@ -0,0 +1 @@
+module.exports = 'a';
diff --git a/test/fixtures/es-module-specifiers/package-type-commonjs/b.mjs b/test/fixtures/es-module-specifiers/package-type-commonjs/b.mjs
new file mode 100644
index 0000000000..137b8ce642
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/package-type-commonjs/b.mjs
@@ -0,0 +1 @@
+export const b = 'b';
diff --git a/test/fixtures/es-module-specifiers/package-type-commonjs/c.cjs b/test/fixtures/es-module-specifiers/package-type-commonjs/c.cjs
new file mode 100644
index 0000000000..2d5312952f
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/package-type-commonjs/c.cjs
@@ -0,0 +1,5 @@
+module.exports = {
+  one: 1,
+  two: 2,
+  three: 3
+};
diff --git a/test/fixtures/es-module-specifiers/package-type-commonjs/index.mjs b/test/fixtures/es-module-specifiers/package-type-commonjs/index.mjs
new file mode 100644
index 0000000000..ef2b30b19b
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/package-type-commonjs/index.mjs
@@ -0,0 +1,21 @@
+// js file that is common.js
+import a from './a.js';
+// ESM with named export
+import {b} from './b.mjs';
+// import 'c.cjs';
+import cjs from './c.cjs';
+// proves cross boundary fun bits
+import jsAsEsm from '../package-type-module/a.js';
+
+// named export from core
+import {strictEqual, deepStrictEqual} from 'assert';
+
+strictEqual(a, jsAsEsm);
+strictEqual(b, 'b');
+deepStrictEqual(cjs, {
+  one: 1,
+  two: 2,
+  three: 3
+});
+
+export default 'commonjs';
diff --git a/test/fixtures/es-module-specifiers/package-type-commonjs/package.json b/test/fixtures/es-module-specifiers/package-type-commonjs/package.json
new file mode 100644
index 0000000000..5bbefffbab
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/package-type-commonjs/package.json
@@ -0,0 +1,3 @@
+{
+  "type": "commonjs"
+}
diff --git a/test/fixtures/es-module-specifiers/package-type-module/a.js b/test/fixtures/es-module-specifiers/package-type-module/a.js
new file mode 100644
index 0000000000..90bd54cd7f
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/package-type-module/a.js
@@ -0,0 +1 @@
+export default 'a'
diff --git a/test/fixtures/es-module-specifiers/package-type-module/b.mjs b/test/fixtures/es-module-specifiers/package-type-module/b.mjs
new file mode 100644
index 0000000000..137b8ce642
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/package-type-module/b.mjs
@@ -0,0 +1 @@
+export const b = 'b';
diff --git a/test/fixtures/es-module-specifiers/package-type-module/c.cjs b/test/fixtures/es-module-specifiers/package-type-module/c.cjs
new file mode 100644
index 0000000000..2d5312952f
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/package-type-module/c.cjs
@@ -0,0 +1,5 @@
+module.exports = {
+  one: 1,
+  two: 2,
+  three: 3
+};
diff --git a/test/fixtures/es-module-specifiers/package-type-module/index.js b/test/fixtures/es-module-specifiers/package-type-module/index.js
new file mode 100644
index 0000000000..a8baacb7c9
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/package-type-module/index.js
@@ -0,0 +1,21 @@
+// ESM with only default
+import a from './a.js';
+// ESM with named export
+import {b} from './b.mjs';
+// import 'c.cjs';
+import cjs from './c.cjs';
+// import across boundaries
+import jsAsCjs from '../package-type-commonjs/a.js'
+
+// named export from core
+import {strictEqual, deepStrictEqual} from 'assert';
+
+strictEqual(a, jsAsCjs);
+strictEqual(b, 'b');
+deepStrictEqual(cjs, {
+  one: 1,
+  two: 2,
+  three: 3
+});
+
+export default 'module';
diff --git a/test/fixtures/es-module-specifiers/package-type-module/package.json b/test/fixtures/es-module-specifiers/package-type-module/package.json
new file mode 100644
index 0000000000..3dbc1ca591
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/package-type-module/package.json
@@ -0,0 +1,3 @@
+{
+  "type": "module"
+}
diff --git a/test/fixtures/es-module-specifiers/package.json b/test/fixtures/es-module-specifiers/package.json
new file mode 100644
index 0000000000..9e26dfeeb6
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/package.json
@@ -0,0 +1 @@
+{}
\ No newline at end of file
diff --git a/test/fixtures/es-modules/cjs-file.cjs b/test/fixtures/es-modules/cjs-file.cjs
new file mode 100644
index 0000000000..3d0637686e
--- /dev/null
+++ b/test/fixtures/es-modules/cjs-file.cjs
@@ -0,0 +1 @@
+console.log('.cjs file');
diff --git a/test/fixtures/es-modules/json-cache/another.cjs b/test/fixtures/es-modules/json-cache/another.cjs
new file mode 100644
index 0000000000..8c8e9f1c0f
--- /dev/null
+++ b/test/fixtures/es-modules/json-cache/another.cjs
@@ -0,0 +1,7 @@
+const test = require('./test.json');
+
+module.exports = {
+  ...test
+};
+
+test.one = 'it comes';
diff --git a/test/fixtures/es-modules/json-cache/mod.cjs b/test/fixtures/es-modules/json-cache/mod.cjs
new file mode 100644
index 0000000000..047cfb24a4
--- /dev/null
+++ b/test/fixtures/es-modules/json-cache/mod.cjs
@@ -0,0 +1,7 @@
+const test = require('./test.json');
+
+module.exports = {
+  ...test
+};
+
+test.one = 'zalgo';
diff --git a/test/fixtures/es-modules/json-cache/test.json b/test/fixtures/es-modules/json-cache/test.json
new file mode 100644
index 0000000000..120cbb2840
--- /dev/null
+++ b/test/fixtures/es-modules/json-cache/test.json
@@ -0,0 +1,5 @@
+{
+  "one": 1,
+  "two": 2,
+  "three": 3
+}
diff --git a/test/fixtures/es-modules/json.json b/test/fixtures/es-modules/json.json
deleted file mode 100644
index 8288d42e2b..0000000000
--- a/test/fixtures/es-modules/json.json
+++ /dev/null
@@ -1,3 +0,0 @@
-{
-  "val": 42
-}
diff --git a/test/fixtures/es-modules/loop.mjs b/test/fixtures/es-modules/loop.mjs
index 1b5cab10ed..3d2ddd2eb7 100644
--- a/test/fixtures/es-modules/loop.mjs
+++ b/test/fixtures/es-modules/loop.mjs
@@ -1,4 +1,4 @@
-import { message } from './message';
+import { message } from './message.mjs';
 
 var t = 1;
 var k = 1;
diff --git a/test/fixtures/es-modules/mjs-file.mjs b/test/fixtures/es-modules/mjs-file.mjs
new file mode 100644
index 0000000000..489d4ab570
--- /dev/null
+++ b/test/fixtures/es-modules/mjs-file.mjs
@@ -0,0 +1 @@
+console.log('.mjs file');
diff --git a/test/fixtures/es-modules/noext-esm b/test/fixtures/es-modules/noext-esm
new file mode 100644
index 0000000000..251d6e538a
--- /dev/null
+++ b/test/fixtures/es-modules/noext-esm
@@ -0,0 +1,2 @@
+export default 'module';
+console.log('executed');
diff --git a/test/fixtures/es-modules/package-type-commonjs/index.js b/test/fixtures/es-modules/package-type-commonjs/index.js
new file mode 100644
index 0000000000..009431d851
--- /dev/null
+++ b/test/fixtures/es-modules/package-type-commonjs/index.js
@@ -0,0 +1,3 @@
+const identifier = 'package-type-commonjs';
+console.log(identifier);
+module.exports = identifier;
diff --git a/test/fixtures/es-modules/package-type-commonjs/package.json b/test/fixtures/es-modules/package-type-commonjs/package.json
new file mode 100644
index 0000000000..4aaa4a2388
--- /dev/null
+++ b/test/fixtures/es-modules/package-type-commonjs/package.json
@@ -0,0 +1,4 @@
+{
+  "type": "commonjs",
+  "main": "index.js"
+}
diff --git a/test/fixtures/es-modules/package-type-module/index.js b/test/fixtures/es-modules/package-type-module/index.js
new file mode 100644
index 0000000000..12aba970ef
--- /dev/null
+++ b/test/fixtures/es-modules/package-type-module/index.js
@@ -0,0 +1,3 @@
+const identifier = 'package-type-module';
+console.log(identifier);
+export default identifier;
diff --git a/test/fixtures/es-modules/package-type-module/package.json b/test/fixtures/es-modules/package-type-module/package.json
new file mode 100644
index 0000000000..07aec65d5a
--- /dev/null
+++ b/test/fixtures/es-modules/package-type-module/package.json
@@ -0,0 +1,4 @@
+{
+  "type": "module",
+  "main": "index.js"
+}
diff --git a/test/fixtures/es-modules/package-without-type/index.js b/test/fixtures/es-modules/package-without-type/index.js
new file mode 100644
index 0000000000..a547216cb0
--- /dev/null
+++ b/test/fixtures/es-modules/package-without-type/index.js
@@ -0,0 +1,3 @@
+const identifier = 'package-without-type';
+console.log(identifier);
+module.exports = identifier;
diff --git a/test/fixtures/es-modules/package-without-type/package.json b/test/fixtures/es-modules/package-without-type/package.json
new file mode 100644
index 0000000000..14ab704d8f
--- /dev/null
+++ b/test/fixtures/es-modules/package-without-type/package.json
@@ -0,0 +1,3 @@
+{
+  "main": "index.js"
+}
diff --git a/test/fixtures/es-modules/pjson-main/main.js b/test/fixtures/es-modules/pjson-main/main.js
deleted file mode 100644
index dfdd47b877..0000000000
--- a/test/fixtures/es-modules/pjson-main/main.js
+++ /dev/null
@@ -1 +0,0 @@
-module.exports = 'main';
diff --git a/test/fixtures/es-modules/pjson-main/main.mjs b/test/fixtures/es-modules/pjson-main/main.mjs
new file mode 100644
index 0000000000..9eb0aade18
--- /dev/null
+++ b/test/fixtures/es-modules/pjson-main/main.mjs
@@ -0,0 +1 @@
+export const main = 'main'
diff --git a/test/fixtures/es-modules/pjson-main/package.json b/test/fixtures/es-modules/pjson-main/package.json
index c13b8cf6ac..ea9b784692 100644
--- a/test/fixtures/es-modules/pjson-main/package.json
+++ b/test/fixtures/es-modules/pjson-main/package.json
@@ -1,3 +1,3 @@
 {
-  "main": "main.js"
+  "main": "main.mjs"
 }
diff --git a/test/fixtures/es-modules/test-esm-double-encoding-native%20.js b/test/fixtures/es-modules/test-esm-double-encoding-native%20.mjs
index ea1caa81be..a3bfe972e5 100644
--- a/test/fixtures/es-modules/test-esm-double-encoding-native%20.js
+++ b/test/fixtures/es-modules/test-esm-double-encoding-native%20.mjs
@@ -3,4 +3,4 @@
 // Trivial test to assert we can load files with `%` in their pathname.
 // Imported by `test-esm-double-encoding.mjs`.
 
-module.exports = 42;
+export default 42;
diff --git a/test/fixtures/experimental.json b/test/fixtures/experimental.json
new file mode 100644
index 0000000000..12611d2385
--- /dev/null
+++ b/test/fixtures/experimental.json
@@ -0,0 +1,3 @@
+{
+  "ofLife": 42
+}
diff --git a/test/fixtures/syntax/bad_syntax.mjs b/test/fixtures/syntax/bad_syntax.mjs
new file mode 100644
index 0000000000..c2cd118b23
--- /dev/null
+++ b/test/fixtures/syntax/bad_syntax.mjs
@@ -0,0 +1 @@
+var foo bar;
diff --git a/test/message/esm_display_syntax_error.out b/test/message/esm_display_syntax_error.out
index 1c68ecb952..5e82a1e1ee 100644
--- a/test/message/esm_display_syntax_error.out
+++ b/test/message/esm_display_syntax_error.out
@@ -2,6 +2,7 @@
 file:///*/test/message/esm_display_syntax_error.mjs:3
 await async () => 0;
 ^^^^^
+
 SyntaxError: Unexpected reserved word
-    at internal/modules/esm/translators.js:*:*
+    at Loader.moduleStrategy (internal/modules/esm/translators.js:*:*)
     at async link (internal/modules/esm/module_job.js:*:*)
diff --git a/test/message/esm_display_syntax_error_import.mjs b/test/message/esm_display_syntax_error_import.mjs
index 87cedf1d4e..12d10270e9 100644
--- a/test/message/esm_display_syntax_error_import.mjs
+++ b/test/message/esm_display_syntax_error_import.mjs
@@ -1,7 +1,7 @@
 // Flags:  --experimental-modules
-/* eslint-disable no-unused-vars */
-import '../common';
+/* eslint-disable no-unused-vars, node-core/required-modules */
+import '../common/index.mjs';
 import {
   foo,
   notfound
-} from '../fixtures/es-module-loaders/module-named-exports';
+} from '../fixtures/es-module-loaders/module-named-exports.mjs';
diff --git a/test/message/esm_display_syntax_error_import.out b/test/message/esm_display_syntax_error_import.out
index edbbde9f2d..a3601d6cb4 100644
--- a/test/message/esm_display_syntax_error_import.out
+++ b/test/message/esm_display_syntax_error_import.out
@@ -2,7 +2,7 @@
 file:///*/test/message/esm_display_syntax_error_import.mjs:6
   notfound
   ^^^^^^^^
-SyntaxError: The requested module '../fixtures/es-module-loaders/module-named-exports' does not provide an export named 'notfound'
+SyntaxError: The requested module '../fixtures/es-module-loaders/module-named-exports.mjs' does not provide an export named 'notfound'
     at ModuleJob._instantiate (internal/modules/esm/module_job.js:*:*)
     at async ModuleJob.run (internal/modules/esm/module_job.js:*:*)
     at async Loader.import (internal/modules/esm/loader.js:*:*)
diff --git a/test/message/esm_display_syntax_error_import_module.mjs b/test/message/esm_display_syntax_error_import_module.mjs
index 32c0edb350..a53bbbcd19 100644
--- a/test/message/esm_display_syntax_error_import_module.mjs
+++ b/test/message/esm_display_syntax_error_import_module.mjs
@@ -1,3 +1,4 @@
 // Flags:  --experimental-modules
-import '../common';
-import '../fixtures/es-module-loaders/syntax-error-import';
+/* eslint-disable node-core/required-modules */
+import '../common/index.mjs';
+import '../fixtures/es-module-loaders/syntax-error-import.mjs';
diff --git a/test/message/esm_display_syntax_error_import_module.out b/test/message/esm_display_syntax_error_import_module.out
index 0512a9ac77..0daaeff5b9 100644
--- a/test/message/esm_display_syntax_error_import_module.out
+++ b/test/message/esm_display_syntax_error_import_module.out
@@ -1,8 +1,8 @@
 (node:*) ExperimentalWarning: The ESM module loader is experimental.
 file:///*/test/fixtures/es-module-loaders/syntax-error-import.mjs:1
-import { foo, notfound } from './module-named-exports';
+import { foo, notfound } from './module-named-exports.mjs';
               ^^^^^^^^
-SyntaxError: The requested module './module-named-exports' does not provide an export named 'notfound'
+SyntaxError: The requested module './module-named-exports.mjs' does not provide an export named 'notfound'
     at ModuleJob._instantiate (internal/modules/esm/module_job.js:*:*)
     at async ModuleJob.run (internal/modules/esm/module_job.js:*:*)
     at async Loader.import (internal/modules/esm/loader.js:*:*)
diff --git a/test/message/esm_display_syntax_error_module.mjs b/test/message/esm_display_syntax_error_module.mjs
index e74b70bec8..5905d2a954 100644
--- a/test/message/esm_display_syntax_error_module.mjs
+++ b/test/message/esm_display_syntax_error_module.mjs
@@ -1,3 +1,4 @@
 // Flags:  --experimental-modules
-import '../common';
-import '../fixtures/es-module-loaders/syntax-error';
+/* eslint-disable node-core/required-modules */
+import '../common/index.mjs';
+import '../fixtures/es-module-loaders/syntax-error.mjs';
diff --git a/test/message/esm_display_syntax_error_module.out b/test/message/esm_display_syntax_error_module.out
index 4e4cbf2ea3..a1498f72c9 100644
--- a/test/message/esm_display_syntax_error_module.out
+++ b/test/message/esm_display_syntax_error_module.out
@@ -2,5 +2,6 @@
 file:///*/test/fixtures/es-module-loaders/syntax-error.mjs:2
 await async () => 0;
 ^^^^^
+
 SyntaxError: Unexpected reserved word
-    at internal/modules/esm/translators.js:*:*
+    at Loader.moduleStrategy (internal/modules/esm/translators.js:*:*)
\ No newline at end of file
diff --git a/test/parallel/test-cli-syntax-piped-bad.js b/test/parallel/test-cli-syntax-piped-bad.js
index 4fb24b24f3..6d6f800a40 100644
--- a/test/parallel/test-cli-syntax-piped-bad.js
+++ b/test/parallel/test-cli-syntax-piped-bad.js
@@ -8,24 +8,45 @@ const node = process.execPath;
 
 // Test both sets of arguments that check syntax
 const syntaxArgs = [
-  ['-c'],
-  ['--check']
+  '-c',
+  '--check'
 ];
 
 // Match on the name of the `Error` but not the message as it is different
 // depending on the JavaScript engine.
-const syntaxErrorRE = /^SyntaxError: \b/m;
+const syntaxErrorRE = /^SyntaxError: Unexpected identifier\b/m;
 
 // Should throw if code piped from stdin with --check has bad syntax
 // loop each possible option, `-c` or `--check`
-syntaxArgs.forEach(function(args) {
+syntaxArgs.forEach(function(arg) {
   const stdin = 'var foo bar;';
-  const c = spawnSync(node, args, { encoding: 'utf8', input: stdin });
+  const c = spawnSync(node, [arg], { encoding: 'utf8', input: stdin });
 
   // stderr should include '[stdin]' as the filename
   assert(c.stderr.startsWith('[stdin]'), `${c.stderr} starts with ${stdin}`);
 
-  // No stdout or stderr should be produced
+  // No stdout should be produced
+  assert.strictEqual(c.stdout, '');
+
+  // stderr should have a syntax error message
+  assert(syntaxErrorRE.test(c.stderr), `${syntaxErrorRE} === ${c.stderr}`);
+
+  assert.strictEqual(c.status, 1);
+});
+
+// Check --entry-type=module
+syntaxArgs.forEach(function(arg) {
+  const stdin = 'export var p = 5; var foo bar;';
+  const c = spawnSync(
+    node,
+    ['--experimental-modules', '--entry-type=module', '--no-warnings', arg],
+    { encoding: 'utf8', input: stdin }
+  );
+
+  // stderr should include '[stdin]' as the filename
+  assert(c.stderr.startsWith('[stdin]'), `${c.stderr} starts with ${stdin}`);
+
+  // No stdout should be produced
   assert.strictEqual(c.stdout, '');
 
   // stderr should have a syntax error message
diff --git a/test/parallel/test-cli-syntax-piped-good.js b/test/parallel/test-cli-syntax-piped-good.js
index cdadf449d8..b2b02172cb 100644
--- a/test/parallel/test-cli-syntax-piped-good.js
+++ b/test/parallel/test-cli-syntax-piped-good.js
@@ -8,15 +8,31 @@ const node = process.execPath;
 
 // Test both sets of arguments that check syntax
 const syntaxArgs = [
-  ['-c'],
-  ['--check']
+  '-c',
+  '--check'
 ];
 
 // Should not execute code piped from stdin with --check.
 // Loop each possible option, `-c` or `--check`.
-syntaxArgs.forEach(function(args) {
+syntaxArgs.forEach(function(arg) {
   const stdin = 'throw new Error("should not get run");';
-  const c = spawnSync(node, args, { encoding: 'utf8', input: stdin });
+  const c = spawnSync(node, [arg], { encoding: 'utf8', input: stdin });
+
+  // No stdout or stderr should be produced
+  assert.strictEqual(c.stdout, '');
+  assert.strictEqual(c.stderr, '');
+
+  assert.strictEqual(c.status, 0);
+});
+
+// Check --entry-type=module
+syntaxArgs.forEach(function(arg) {
+  const stdin = 'export var p = 5; throw new Error("should not get run");';
+  const c = spawnSync(
+    node,
+    ['--experimental-modules', '--no-warnings', '--entry-type=module', arg],
+    { encoding: 'utf8', input: stdin }
+  );
 
   // No stdout or stderr should be produced
   assert.strictEqual(c.stdout, '');
diff --git a/test/parallel/test-loaders-unknown-builtin-module.mjs b/test/parallel/test-loaders-unknown-builtin-module.mjs
index db3cfa3582..5f47f191f5 100644
--- a/test/parallel/test-loaders-unknown-builtin-module.mjs
+++ b/test/parallel/test-loaders-unknown-builtin-module.mjs
@@ -1,5 +1,6 @@
 // Flags: --experimental-modules --loader ./test/fixtures/es-module-loaders/loader-unknown-builtin-module.mjs
-import { expectsError, mustCall } from '../common';
+/* eslint-disable node-core/required-modules */
+import { expectsError, mustCall } from '../common/index.mjs';
 import assert from 'assert';
 
 const unknownBuiltinModule = 'unknown-builtin-module';
diff --git a/test/parallel/test-module-main-extension-lookup.js b/test/parallel/test-module-main-extension-lookup.js
index 3d20316647..9e7eab295e 100644
--- a/test/parallel/test-module-main-extension-lookup.js
+++ b/test/parallel/test-module-main-extension-lookup.js
@@ -6,6 +6,6 @@ const { execFileSync } = require('child_process');
 const node = process.argv[0];
 
 execFileSync(node, ['--experimental-modules',
-                    fixtures.path('es-modules', 'test-esm-ok')]);
+                    fixtures.path('es-modules', 'test-esm-ok.mjs')]);
 execFileSync(node, ['--experimental-modules',
                     fixtures.path('es-modules', 'noext')]);