perf(ngClass): optimize the case of static map of classes with large objects

Author: drpicox

src/ng/directive/ngClass.js

@@ -1,14 +1,16 @@
 'use strict';
 
 function classDirective(name, selector) {
+  var staticMapClassRegEx = /^\s*\{/;
   name = 'ngClass' + name;
   return ['$animate', function($animate) {
     return {
       restrict: 'AC',
       link: function(scope, element, attr) {
         var oldVal;
 
-        scope.$watch(attr[name], ngClassWatchAction, true);
+        // shortcut: if it is clearly a map of classes do not copy values, they are supposed to be boolean (truly/falsy)
+        scope[staticMapClassRegEx.test(attr[name]) ? '$watchCollection' : '$watch'](attr[name], ngClassWatchAction, true);
 
         attr.$observe('class', function(value) {
           ngClassWatchAction(scope.$eval(attr[name]));

test/ng/directive/ngClassSpec.js

@@ -409,6 +409,15 @@ describe('ngClass', function() {
     expect(e2.hasClass('even')).toBeTruthy();
     expect(e2.hasClass('odd')).toBeFalsy();
   }));
+
+  it('should not copy large objects via hard map of classes', inject(function($rootScope, $compile) {
+    element = $compile('<div ng-class="{foo: verylargeobject}"></div>')($rootScope);
+    $rootScope.verylargeobject = {very: 'largeobject'};
+    $rootScope.$digest();
+
+    expect($rootScope.$$watchers[0].last).toEqual(jasmine.any(Number));
+  }));
+
 });
 
 describe('ngClass animations', function() {