seq callback is now optional. closes #618

3 files changed, 31 insertions, 3 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index d637ab4..83c1230 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,7 @@ New Features:
 - Added `ensureAsync` - A wrapper that ensures an async function calls its callback on a later tick. (#769)
 - Optimized `map`, `eachOf`, and `waterfall` families of functions
 - Passing a `null` or `undefined` array to `map`, `each`, `parallel` and families will be treated as an empty array (#667).
+- The callback is not optional for the composed results of `compose` and `seq`. (#618)
 - Reduced file size by 4kb, (minified version by 1kb) 
 - Added code coverage through `nyc` and `coveralls` (#768)
 
diff --git a/lib/async.js b/lib/async.js
index 58b11d9..abc1f7b 100644
--- a/lib/async.js
+++ b/lib/async.js
@@ -335,7 +335,7 @@
     }
 
     function _asyncMap(eachfn, arr, iterator, callback) {
-        callback = callback || noop;
+        callback = _once(callback || noop);
         var results = [];
         eachfn(arr, function (value, index, callback) {
             iterator(value, function (err, v) {
@@ -822,7 +822,7 @@
             _arrayEach(data, function(task) {
                 var item = {
                     data: task,
-                    callback: typeof callback === 'function' ? callback : noop
+                    callback: callback || noop
                 };
 
                 if (pos) {
@@ -1077,7 +1077,14 @@
         return function () {
             var that = this;
             var args = _baseSlice(arguments);
-            var callback = args.pop();
+
+            var callback = args.slice(-1)[0];
+            if (typeof callback == 'function') {
+                args.pop();
+            } else {
+                callback = noop;
+            }
+
             async.reduce(fns, args, function (newargs, fn, cb) {
                 fn.apply(that, newargs.concat([function () {
                     var err = arguments[0];
diff --git a/test/test-async.js b/test/test-async.js
index 2fe11bd..670d14a 100755
--- a/test/test-async.js
+++ b/test/test-async.js
@@ -387,6 +387,26 @@ exports['seq binding'] = function (test) {
     });
 };
 
+exports['seq without callback'] = function (test) {
+    test.expect(2);
+    var testcontext = {name: 'foo'};
+
+    var add2 = function (n, cb) {
+        test.equal(this, testcontext);
+        setTimeout(function () {
+            cb(null, n + 2);
+        }, 50);
+    };
+    var mul3 = function () {
+        test.equal(this, testcontext);
+        setTimeout(function () {
+            test.done();
+        }, 15);
+    };
+    var add2mul3 = async.seq(add2, mul3);
+    add2mul3.call(testcontext, 3);
+};
+
 exports['auto'] = function(test){
     var callOrder = [];
     async.auto({