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*(::)?\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 +409,37 @@ describe('ngClass', function() {
     expect(e2.hasClass('even')).toBeTruthy();
     expect(e2.hasClass('odd')).toBeFalsy();
   }));
+
+  describe('large objects', function() {
+
+    var verylargeobject, getProp;
+    beforeEach(function() {
+      getProp = jasmine.createSpy('getProp');
+      verylargeobject = {};
+      Object.defineProperty(verylargeobject, 'prop', {
+        get: getProp,
+        enumerable: true
+      });
+    });
+
+    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 = verylargeobject;
+      $rootScope.$digest();
+
+      expect(getProp).not.toHaveBeenCalled();
+    }));
+
+    it('should not copy large objects via hard map of classes in one-time binding', inject(function($rootScope, $compile) {
+      element = $compile('<div ng-class="::{foo: verylargeobject}"></div>')($rootScope);
+      $rootScope.verylargeobject = verylargeobject;
+      $rootScope.$digest();
+
+      expect(getProp).not.toHaveBeenCalled();
+    }));
+  });
+
+
 });
 
 describe('ngClass animations', function() {