perf(jqLite): implement and use the empty method in place of html(‘’)

jQuery's elem.html('') is way slower than elem.empty(). As clearing
element contents happens quite often in certain scenarios, switching
to using .empty() provides a significant performance boost when using
Angular with jQuery.

Closes #4457

docs/component-spec/annotationsSpec.js

@@ -5,7 +5,7 @@ describe('Docs Annotations', function() {
   var body;
   beforeEach(function() {
     body = angular.element(document.body);
-    body.html('');
+    body.empty();
   });
 
   var normalizeHtml = function(html) {

docs/components/angular-bootstrap/bootstrap-prettify.js

@@ -28,7 +28,7 @@ function escape(text) {
 function setHtmlIe8SafeWay(element, html) {
   var newElement = angular.element('<pre>' + html + '</pre>');
 
-  element.html('');
+  element.empty();
   element.append(newElement.contents());
   return element;
 }

docs/content/guide/dev_guide.unit-testing.ngdoc

@@ -222,7 +222,7 @@ var pc = new PasswordCtrl();
 input.val('abc');
 pc.grade();
 expect(span.text()).toEqual('weak');
-$('body').html('');
+$('body').empty();
 </pre>
 
 In angular the controllers are strictly separated from the DOM manipulation logic and this results in

src/Angular.js

@@ -974,7 +974,7 @@ function startingTag(element) {
   try {
     // turns out IE does not let you set .html() on elements which
     // are not allowed to have children. So we just ignore it.
-    element.html('');
+    element.empty();
   } catch(e) {}
   // As Per DOM Standards
   var TEXT_NODE = 3;

src/jqLite.js

@@ -46,6 +46,7 @@
  * - [`contents()`](http://api.jquery.com/contents/)
  * - [`css()`](http://api.jquery.com/css/)
  * - [`data()`](http://api.jquery.com/data/)
+ * - [`empty()`](http://api.jquery.com/empty/)
  * - [`eq()`](http://api.jquery.com/eq/)
  * - [`find()`](http://api.jquery.com/find/) - Limited to lookups by tag name
  * - [`hasClass()`](http://api.jquery.com/hasClass/)
@@ -358,6 +359,15 @@ function jqLiteInheritedData(element, name, value) {
   }
 }
 
+function jqLiteEmpty(element) {
+  for (var i = 0, childNodes = element.childNodes; i < childNodes.length; i++) {
+    jqLiteDealoc(childNodes[i]);
+  }
+  while (element.firstChild) {
+    element.removeChild(element.firstChild);
+  }
+}
+
 //////////////////////////////////////////
 // Functions which are declared directly.
 //////////////////////////////////////////
@@ -552,7 +562,9 @@ forEach({
       jqLiteDealoc(childNodes[i]);
     }
     element.innerHTML = value;
-  }
+  },
+
+  empty: jqLiteEmpty
 }, function(fn, name){
   /**
    * Properties: writes return selection, reads return first value
@@ -562,11 +574,13 @@ forEach({
 
     // jqLiteHasClass has only two arguments, but is a getter-only fn, so we need to special-case it
     // in a way that survives minification.
-    if (((fn.length == 2 && (fn !== jqLiteHasClass && fn !== jqLiteController)) ? arg1 : arg2) === undefined) {
+    // jqLiteEmpty takes no arguments but is a setter.
+    if (fn !== jqLiteEmpty &&
+        (((fn.length == 2 && (fn !== jqLiteHasClass && fn !== jqLiteController)) ? arg1 : arg2) === undefined)) {
       if (isObject(arg1)) {
 
         // we are a write, but the object properties are the key/values
-        for(i=0; i < this.length; i++) {
+        for (i = 0; i < this.length; i++) {
           if (fn === jqLiteData) {
             // data() takes the whole object in jQuery
             fn(this[i], arg1);
@@ -591,7 +605,7 @@ forEach({
       }
     } else {
       // we are a write, so apply to all children
-      for(i=0; i < this.length; i++) {
+      for (i = 0; i < this.length; i++) {
         fn(this[i], arg1, arg2);
       }
       // return self for chaining

src/ng/compile.js

@@ -1219,7 +1219,7 @@ function $CompileProvider($provide, $$sanitizeUriProvider) {
                                         });
           } else {
             $template = jqLite(jqLiteClone(compileNode)).contents();
-            $compileNode.html(''); // clear contents
+            $compileNode.empty(); // clear contents
             childTranscludeFn = compile($template, transcludeFn);
           }
         }
@@ -1651,7 +1651,7 @@ function $CompileProvider($provide, $$sanitizeUriProvider) {
               ? origAsyncDirective.templateUrl($compileNode, tAttrs)
               : origAsyncDirective.templateUrl;
 
-      $compileNode.html('');
+      $compileNode.empty();
 
       $http.get($sce.getTrustedResourceUrl(templateUrl), {cache: $templateCache}).
         success(function(content) {

src/ng/directive/ngTransclude.js

@@ -69,7 +69,7 @@ var ngTranscludeDirective = ngDirective({
 
   link: function($scope, $element, $attrs, controller) {
     controller.$transclude(function(clone) {
-      $element.html('');
+      $element.empty();
       $element.append(clone);
     });
   }

src/ng/directive/select.js

@@ -333,13 +333,13 @@ var selectDirective = ['$compile', '$parse', function($compile,   $parse) {
           // becomes the compilation root
           nullOption.removeClass('ng-scope');
 
-          // we need to remove it before calling selectElement.html('') because otherwise IE will
+          // we need to remove it before calling selectElement.empty() because otherwise IE will
           // remove the label from the element. wtf?
           nullOption.remove();
         }
 
         // clear contents, we'll add what's needed based on the model
-        selectElement.html('');
+        selectElement.empty();
 
         selectElement.on('change', function() {
           scope.$apply(function() {

src/ngAnimate/animate.js

@@ -1237,7 +1237,7 @@ angular.module('ngAnimate', ['ng'])
           //make the element super hidden and override any CSS style values
           clone.attr('style','position:absolute; top:-9999px; left:-9999px');
           clone.removeAttr('id');
-          clone.html('');
+          clone.empty();
 
           forEach(oldClasses.split(' '), function(klass) {
             clone.removeClass(klass);

test/helpers/testabilityPatch.js

@@ -29,8 +29,7 @@ beforeEach(function() {
     bindJQuery();
   }
 
-
-  angular.element(document.body).html('').removeData();
+  angular.element(document.body).empty().removeData();
 });
 
 afterEach(function() {

test/jqLiteSpec.js

@@ -322,7 +322,7 @@ describe('jqLite', function() {
     });
 
 
-    it('should emit $destroy event if an element is removed via html()', inject(function(log) {
+    it('should emit $destroy event if an element is removed via html(\'\')', inject(function(log) {
       var element = jqLite('<div><span>x</span></div>');
       element.find('span').on('$destroy', log.fn('destroyed'));
 
@@ -333,6 +333,17 @@ describe('jqLite', function() {
     }));
 
 
+    it('should emit $destroy event if an element is removed via empty()', inject(function(log) {
+      var element = jqLite('<div><span>x</span></div>');
+      element.find('span').on('$destroy', log.fn('destroyed'));
+
+      element.empty();
+
+      expect(element.html()).toBe('');
+      expect(log).toEqual('destroyed');
+    }));
+
+
     it('should retrieve all data if called without params', function() {
       var element = jqLite(a);
       expect(element.data()).toEqual({});
@@ -786,7 +797,7 @@ describe('jqLite', function() {
     });
 
 
-    it('should read/write value', function() {
+    it('should read/write a value', function() {
       var element = jqLite('<div>abc</div>');
       expect(element.length).toEqual(1);
       expect(element[0].innerHTML).toEqual('abc');
@@ -797,6 +808,16 @@ describe('jqLite', function() {
   });
 
 
+  describe('empty', function() {
+    it('should write a value', function() {
+      var element = jqLite('<div>abc</div>');
+      expect(element.length).toEqual(1);
+      expect(element.empty() == element).toBeTruthy();
+      expect(element.html()).toEqual('');
+    });
+  });
+
+
   describe('on', function() {
     it('should bind to window on hashchange', function() {
       if (jqLite.fn) return; // don't run in jQuery

test/ng/compileSpec.js

@@ -170,26 +170,26 @@ describe('$compile', function() {
       // First with only elements at the top level
       element = jqLite('<div><div></div></div>');
       $compile(element.contents())($rootScope);
-      element.html('');
+      element.empty();
       expect(calcCacheSize()).toEqual(0);
 
       // Next with non-empty text nodes at the top level
       // (in this case the compiler will wrap them in a <span>)
       element = jqLite('<div>xxx</div>');
       $compile(element.contents())($rootScope);
-      element.html('');
+      element.empty();
       expect(calcCacheSize()).toEqual(0);
 
       // Next with comment nodes at the top level
       element = jqLite('<div><!-- comment --></div>');
       $compile(element.contents())($rootScope);
-      element.html('');
+      element.empty();
       expect(calcCacheSize()).toEqual(0);
 
       // Finally with empty text nodes at the top level
       element = jqLite('<div>   \n<div></div>   </div>');
       $compile(element.contents())($rootScope);
-      element.html('');
+      element.empty();
       expect(calcCacheSize()).toEqual(0);
     });
 

test/ng/directive/formSpec.js

@@ -216,7 +216,7 @@ describe('form', function() {
         // yes, I know, scope methods should not do direct DOM manipulation, but I wanted to keep
         // this test small. Imagine that the destroy action will cause a model change (e.g.
         // $location change) that will cause some directive to destroy the dom (e.g. ngView+$route)
-        doc.html('');
+        doc.empty();
         destroyed = true;
       }
 

test/ng/directive/ngIncludeSpec.js

@@ -47,7 +47,7 @@ describe('ngInclude', function() {
     $rootScope.url = 'myUrl';
     $rootScope.$digest();
     expect(body.text()).toEqual('misko');
-    body.html('');
+    body.empty();
   }));
 
 
@@ -60,7 +60,7 @@ describe('ngInclude', function() {
     $rootScope.url = 'myUrl';
     $rootScope.$digest();
     expect(element.text()).toEqual('Alibaba');
-    jqLite(document.body).html('');
+    jqLite(document.body).empty();
   }));
 
 
@@ -74,7 +74,7 @@ describe('ngInclude', function() {
     expect(function() { $rootScope.$digest(); }).toThrowMinErr(
         '$sce', 'insecurl',
         /Blocked loading resource from url not allowed by \$sceDelegate policy.  URL: http:\/\/example.com\/myUrl.*/);
-    jqLite(document.body).html('');
+    jqLite(document.body).empty();
   }));
 
 
@@ -88,7 +88,7 @@ describe('ngInclude', function() {
     expect(function() { $rootScope.$digest(); }).toThrowMinErr(
         '$sce', 'insecurl',
         /Blocked loading resource from url not allowed by \$sceDelegate policy.  URL: http:\/\/example.com\/myUrl.*/);
-    jqLite(document.body).html('');
+    jqLite(document.body).empty();
   }));
 
 

test/ngAnimate/animateSpec.js

@@ -301,7 +301,7 @@ describe("ngAnimate", function() {
           inject(function($animate, $compile, $rootScope, $timeout, $sniffer) {
 
           $rootScope.$digest();
-          element.html('');
+          element.empty();
 
           var child1 = $compile('<div>1</div>')($rootScope);
           var child2 = $compile('<div>2</div>')($rootScope);

test/ngScenario/dslSpec.js

@@ -53,7 +53,7 @@ describe("angular.scenario.dsl", function() {
     // Just use the real one since it delegates to this.addFuture
     $root.addFutureAction = angular.scenario.
       SpecRunner.prototype.addFutureAction;
-    jqLite($window.document).html('');
+    jqLite($window.document).empty();
   }));
 
   afterEach(function(){

test/ngTouch/directive/ngClickSpec.js

@@ -152,7 +152,7 @@ describe('ngClick (touch)', function() {
     }));
 
     afterEach(inject(function($document) {
-      $document.find('body').html('');
+      $document.find('body').empty();
     }));