fix($animate): ensure that class-based animations only consider the most recent DOM operations

Prior to this fix $animate would maintain a count of each time a class was
added and removed within $animate. With this fix, $animate instead only cares
about the most recent class times that the classes were added and/or removed
and it will only remember a total of one addClass or removeClass operation per
className.

```
// before
addClass    => +1
removeClass => 0
addClass    => +1
addClass    => +2
removeClass => +1
// this will cause an addClass animation

// now
addClass    => +1
removeClass => 0
addClass    => +1
addClass    => +1
removeClass => 0
// this will cause no animation to run
```

Closes angular#8946

Author: matsko

src/ngAnimate/animate.js

@@ -469,31 +469,16 @@ angular.module('ngAnimate', ['ng'])
 
       function resolveElementClasses(element, cache, runningAnimations) {
         runningAnimations = runningAnimations || {};
-        var map = {};
 
-        forEach(cache.add, function(className) {
-          if (className && className.length) {
-            map[className] = map[className] || 0;
-            map[className]++;
-          }
-        });
-
-        forEach(cache.remove, function(className) {
-          if (className && className.length) {
-            map[className] = map[className] || 0;
-            map[className]--;
-          }
-        });
-
-        var lookup = [];
+        var lookup = {};
         forEach(runningAnimations, function(data, selector) {
           forEach(selector.split(' '), function(s) {
             lookup[s]=data;
           });
         });
 
         var toAdd = [], toRemove = [];
-        forEach(map, function(status, className) {
+        forEach(cache.classes, function(status, className) {
           var hasClass = angular.$$hasClass(element[0], className);
           var matchingAnimation = lookup[className] || {};
 
@@ -505,12 +490,12 @@ angular.module('ngAnimate', ['ng'])
           // Once an animation is allowed then the code will also check to see if
           // there exists any on-going animation that is already adding or remvoing
           // the matching CSS class.
-          if (status < 0) {
+          if (status === false) {
             //does it have the class or will it have the class
             if (hasClass || matchingAnimation.event == 'addClass') {
               toRemove.push(className);
             }
-          } else if (status > 0) {
+          } else if (status === true) {
             //is the class missing or will it be removed?
             if (!hasClass || matchingAnimation.event == 'removeClass') {
               toAdd.push(className);
@@ -997,20 +982,32 @@ angular.module('ngAnimate', ['ng'])
             return $delegate.setClass(element, add, remove);
           }
 
+          // we're using a combined array for both the add and remove
+          // operations since the ORDER OF addClass and removeClass matters
+          var classes, cache = element.data(STORAGE_KEY);
+          var hasCache = !!cache;
+          if (!cache) {
+            cache = {};
+            cache.classes = {};
+          }
+          classes = cache.classes;
+
           add = isArray(add) ? add : add.split(' ');
-          remove = isArray(remove) ? remove : remove.split(' ');
+          forEach(add, function(c) {
+            c && c.length && (classes[c] = true);
+          });
 
-          var cache = element.data(STORAGE_KEY);
-          if (cache) {
-            cache.add = cache.add.concat(add);
-            cache.remove = cache.remove.concat(remove);
+          remove = isArray(remove) ? remove : remove.split(' ');
+          forEach(remove, function(c) {
+            c && c.length && (classes[c] = false);
+          });
 
+          if (hasCache) {
             //the digest cycle will combine all the animations into one function
             return cache.promise;
           } else {
             element.data(STORAGE_KEY, cache = {
-              add : add,
-              remove : remove
+              classes : classes
             });
           }
 

test/ngAnimate/animateSpec.js

@@ -3408,11 +3408,76 @@ describe("ngAnimate", function() {
         $animate.triggerReflow();
 
         expect(log.length).toBe(2);
-        expect(log[0]).toEqual({ name : 'addClass', className : 'one five' });
+        expect(log[0]).toEqual({ name : 'addClass', className : 'one four five' });
         expect(log[1]).toEqual({ name : 'removeClass', className : 'three' });
       });
     });
 
+    it('should intelligently cancel out redundant class-based animations', function() {
+      var log = [];
+      var track = function(name) {
+        return function() {
+          log.push({ name : name, className : arguments[1] });
+        };
+      };
+      module(function($animateProvider) {
+        $animateProvider.register('.animate', function() {
+          return {
+            addClass    : track('addClass'),
+            removeClass : track('removeClass')
+          };
+        });
+      });
+      inject(function($rootScope, $animate, $compile, $rootElement, $document) {
+        $animate.enabled(true);
+
+        var element = $compile('<div class="animate three four"></div>')($rootScope);
+        $rootElement.append(element);
+        angular.element($document[0].body).append($rootElement);
+
+        $animate.removeClass(element, 'one');
+        $rootScope.$digest();
+        $animate.triggerReflow();
+        expect(log.length).toBe(0);
+        $animate.triggerCallbacks();
+
+        $animate.addClass(element, 'two');
+        $animate.addClass(element, 'two');
+        $animate.removeClass(element, 'two');
+        $rootScope.$digest();
+        $animate.triggerReflow();
+        expect(log.length).toBe(0);
+        $animate.triggerCallbacks();
+
+        $animate.removeClass(element, 'three');
+        $animate.addClass(element, 'three');
+        $rootScope.$digest();
+        $animate.triggerReflow();
+        expect(log.length).toBe(0);
+        $animate.triggerCallbacks();
+
+        $animate.removeClass(element, 'four');
+        $animate.addClass(element, 'four');
+        $animate.removeClass(element, 'four');
+        $rootScope.$digest();
+        $animate.triggerReflow();
+        expect(log.length).toBe(1);
+        $animate.triggerCallbacks();
+        expect(log[0]).toEqual({ name : 'removeClass', className : 'four' });
+
+        $animate.addClass(element, 'five');
+        $animate.addClass(element, 'five');
+        $animate.addClass(element, 'five');
+        $animate.removeClass(element, 'five');
+        $animate.addClass(element, 'five');
+        $rootScope.$digest();
+        $animate.triggerReflow();
+        expect(log.length).toBe(2);
+        $animate.triggerCallbacks();
+        expect(log[1]).toEqual({ name : 'addClass', className : 'five' });
+      });
+    });
+
     it('should skip class-based animations if the element is removed before the digest occurs', function() {
       var spy = jasmine.createSpy();
       module(function($animateProvider) {