From 9fb359d412d0e624a10833dc70bcb986ed8e8d02 Mon Sep 17 00:00:00 2001
From: Lucas Galfaso <lgalfaso@gmail.com>
Date: Mon, 10 Aug 2015 10:23:39 +0200
Subject: [PATCH] perf($q): small $q performance optimization

Only generate a new promise when `then` receives some non-undefined parameter
---
 lib/promises-aplus/promises-aplus-test-adapter.js | 2 ++
 src/ng/q.js                                       | 3 +++
 2 files changed, 5 insertions(+)

diff --git a/lib/promises-aplus/promises-aplus-test-adapter.js b/lib/promises-aplus/promises-aplus-test-adapter.js
index 6189dd27e0d2..169d3403e065 100644
--- a/lib/promises-aplus/promises-aplus-test-adapter.js
+++ b/lib/promises-aplus/promises-aplus-test-adapter.js
@@ -4,6 +4,8 @@
 var isFunction = function isFunction(value){return typeof value == 'function';};
 var isPromiseLike = function isPromiseLike(obj) {return obj && isFunction(obj.then);};
 var isObject = function isObject(value){return value != null && typeof value === 'object';};
+var isUndefined = function isUndefined(value) {return typeof value === 'undefined';};
+
 var minErr = function minErr (module, constructor) {
   return function (){
     var ErrorConstructor = constructor || Error;
diff --git a/src/ng/q.js b/src/ng/q.js
index 8713ecb705a2..9466a2e9384d 100644
--- a/src/ng/q.js
+++ b/src/ng/q.js
@@ -274,6 +274,9 @@ function qFactory(nextTick, exceptionHandler) {
 
   extend(Promise.prototype, {
     then: function(onFulfilled, onRejected, progressBack) {
+      if (isUndefined(onFulfilled) && isUndefined(onRejected) && isUndefined(progressBack)) {
+        return this;
+      }
       var result = new Deferred();
 
       this.$$state.pending = this.$$state.pending || [];