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

17 files changed, 64 insertions, 30 deletions

diff --git a/docs/component-spec/annotationsSpec.js b/docs/component-spec/annotationsSpec.js
index a2a78077..60b17d9a 100644
--- a/docs/component-spec/annotationsSpec.js
+++ b/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) {
diff --git a/docs/components/angular-bootstrap/bootstrap-prettify.js b/docs/components/angular-bootstrap/bootstrap-prettify.js
index 43248943..72c136d1 100644
--- a/docs/components/angular-bootstrap/bootstrap-prettify.js
+++ b/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;
 }
diff --git a/docs/content/guide/dev_guide.unit-testing.ngdoc b/docs/content/guide/dev_guide.unit-testing.ngdoc
index 9d3d9765..e15edeb7 100644
--- a/docs/content/guide/dev_guide.unit-testing.ngdoc
+++ b/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
diff --git a/src/Angular.js b/src/Angular.js
index b09d3a7f..e32c3739 100644
--- a/src/Angular.js
+++ b/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;
diff --git a/src/jqLite.js b/src/jqLite.js
index e7531fb3..8a45f966 100644
--- a/src/jqLite.js
+++ b/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
diff --git a/src/ng/compile.js b/src/ng/compile.js
index a6bcc3e7..0af76a75 100644
--- a/src/ng/compile.js
+++ b/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) {
diff --git a/src/ng/directive/ngTransclude.js b/src/ng/directive/ngTransclude.js
index 490ea21f..8eefb6ff 100644
--- a/src/ng/directive/ngTransclude.js
+++ b/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();
       $element.append(clone);
     });
   }
diff --git a/src/ng/directive/select.js b/src/ng/directive/select.js
index 86e04242..d87fa5d3 100644
--- a/src/ng/directive/select.js
+++ b/src/ng/directive/select.js
@@ -333,13 +333,13 @@ var selectDirective = ['$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() {
diff --git a/src/ngAnimate/animate.js b/src/ngAnimate/animate.js
index 8ff7b429..aeb6e32e 100644
--- a/src/ngAnimate/animate.js
+++ b/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);
diff --git a/test/helpers/testabilityPatch.js b/test/helpers/testabilityPatch.js
index 41b5042a..f61be4ee 100644
--- a/test/helpers/testabilityPatch.js
+++ b/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() {
diff --git a/test/jqLiteSpec.js b/test/jqLiteSpec.js
index 09be1c1c..c4f47dcd 100644
--- a/test/jqLiteSpec.js
+++ b/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
diff --git a/test/ng/compileSpec.js b/test/ng/compileSpec.js
index 853290a6..1b98cd58 100755
--- a/test/ng/compileSpec.js
+++ b/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);
     });
 
diff --git a/test/ng/directive/formSpec.js b/test/ng/directive/formSpec.js
index 77beb2fd..dde6f0a0 100644
--- a/test/ng/directive/formSpec.js
+++ b/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;
       }
 
diff --git a/test/ng/directive/ngIncludeSpec.js b/test/ng/directive/ngIncludeSpec.js
index 9e0a47b0..79e7f312 100644
--- a/test/ng/directive/ngIncludeSpec.js
+++ b/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();
   }));
 
 
diff --git a/test/ngAnimate/animateSpec.js b/test/ngAnimate/animateSpec.js
index 44b623b4..01589da1 100644
--- a/test/ngAnimate/animateSpec.js
+++ b/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);
diff --git a/test/ngScenario/dslSpec.js b/test/ngScenario/dslSpec.js
index f94ec583..2553fadd 100644
--- a/test/ngScenario/dslSpec.js
+++ b/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(){
diff --git a/test/ngTouch/directive/ngClickSpec.js b/test/ngTouch/directive/ngClickSpec.js
index 0eccc8f3..43735709 100644
--- a/test/ngTouch/directive/ngClickSpec.js
+++ b/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();
     }));