feat(q): add isPromiseLike

- Add `isPromiseLike` public method for determining whether value is a promise-like object

Author: wesleycho

src/Angular.js

@@ -674,7 +674,7 @@ function isBoolean(value) {
 
 
 function isPromiseLike(obj) {
-  return obj && isFunction(obj.then);
+  return (isObject(obj) || isFunction(obj)) && isFunction(obj.then);
 }
 
 

src/ng/q.js

@@ -350,14 +350,12 @@ function qFactory(nextTick, exceptionHandler) {
     },
 
     $$resolve: function(val) {
-      var then;
       var that = this;
       var done = false;
       try {
-        if ((isObject(val) || isFunction(val))) then = val && val.then;
-        if (isFunction(then)) {
+        if (isPromiseLike(val)) {
           this.promise.$$state.status = -1;
-          then.call(val, resolvePromise, rejectPromise, simpleBind(this, this.notify));
+          val.then(resolvePromise, rejectPromise, simpleBind(this, this.notify));
         } else {
           this.promise.$$state.value = val;
           this.promise.$$state.status = 1;
@@ -561,6 +559,22 @@ function qFactory(nextTick, exceptionHandler) {
     return deferred.promise;
   }
 
+  /**
+   * @ngdoc method
+   * @name $q#isPromiseLike
+   * @kind function
+   *
+   * @description
+   * Determines whether object or function is like a promise
+   *
+   * @param {*} value Reference to check
+   * @returns {boolean} True if `value` is promise-like
+   */
+
+  function isPromiseLike(obj) {
+    return (isObject(obj) || isFunction(obj)) && isFunction(obj.then);
+  }
+
   var $Q = function Q(resolver) {
     if (!isFunction(resolver)) {
       throw $qMinErr('norslvr', "Expected resolverFn, got '{0}'", resolver);
@@ -590,6 +604,7 @@ function qFactory(nextTick, exceptionHandler) {
   $Q.when = when;
   $Q.resolve = resolve;
   $Q.all = all;
+  $Q.isPromiseLike = isPromiseLike;
 
   return $Q;
 }

src/ngAnimate/shared.js

@@ -69,10 +69,6 @@ var ANIMATION_DURATION_PROP = ANIMATION_PROP + DURATION_KEY;
 var TRANSITION_DELAY_PROP = TRANSITION_PROP + DELAY_KEY;
 var TRANSITION_DURATION_PROP = TRANSITION_PROP + DURATION_KEY;
 
-var isPromiseLike = function(p) {
-  return p && p.then ? true : false;
-};
-
 var ngMinErr = angular.$$minErr('ng');
 function assertArg(arg, name, reason) {
   if (!arg) {

test/ng/qSpec.js

@@ -1972,6 +1972,26 @@ describe('q', function() {
     });
   });
 
+  describe('isPromiseLike', function() {
+    it('should return false if not returned an object with then method', function() {
+      expect(q.isPromiseLike(1)).toBe(false);
+      expect(q.isPromiseLike('foo')).toBe(false);
+      expect(q.isPromiseLike({})).toBe(false);
+      expect(q.isPromiseLike(function() {})).toBe(false);
+    });
+
+    it('should return true if passed an object with then method', function() {
+      expect(q.isPromiseLike({then: angular.noop})).toBe(true);
+    });
+
+    it('should return true if passed a function with then method', function() {
+      function foo() {}
+      foo.then = angular.noop;
+
+      expect(q.isPromiseLike(foo)).toBe(true);
+    });
+  });
+
   describe('exception logging', function() {
     var mockExceptionLogger = {
       log: [],