fix(checkbox): avoid potential memory leaks, general cleanup

* Avoids potential memory leaks in the checkbox component by removing any event handlers from the `compile` function and avoiding references between `compile` and `link`.
* Cleans out a few redundancies in the checkbox link function.

Fixes #7993.

Closes #9130

Author: crisbeto

src/components/checkbox/checkbox.js

@@ -31,10 +31,10 @@ angular
  * @param {expression=} md-indeterminate This determines when the checkbox should be rendered as 'indeterminate'.
  *     If a truthy expression or no value is passed in the checkbox renders in the md-indeterminate state.
  *     If falsy expression is passed in it just looks like a normal unchecked checkbox.
- *     The indeterminate, checked, and unchecked states are mutually exclusive. A box cannot be in any two states at the same time. 
- *     Adding the 'md-indeterminate' attribute overrides any checked/unchecked rendering logic. 
+ *     The indeterminate, checked, and unchecked states are mutually exclusive. A box cannot be in any two states at the same time.
+ *     Adding the 'md-indeterminate' attribute overrides any checked/unchecked rendering logic.
  *     When using the 'md-indeterminate' attribute use 'ng-checked' to define rendering logic instead of using 'ng-model'.
- * @param {expression=} ng-checked If this expression evaluates as truthy, the 'md-checked' css class is added to the checkbox and it 
+ * @param {expression=} ng-checked If this expression evaluates as truthy, the 'md-checked' css class is added to the checkbox and it
  *     will appear checked.
  *
  * @usage
@@ -56,7 +56,6 @@ angular
  */
 function MdCheckboxDirective(inputDirective, $mdAria, $mdConstant, $mdTheming, $mdUtil, $timeout) {
   inputDirective = inputDirective[0];
-  var CHECKED_CSS = 'md-checked';
 
   return {
     restrict: 'E',
@@ -76,32 +75,35 @@ function MdCheckboxDirective(inputDirective, $mdAria, $mdConstant, $mdTheming, $
   // **********************************************************
 
   function compile (tElement, tAttrs) {
-    var container = tElement.children();
-    var mdIndeterminateStateEnabled = $mdUtil.parseAttributeBoolean(tAttrs.mdIndeterminate);
-
     tAttrs.$set('tabindex', tAttrs.tabindex || '0');
     tAttrs.$set('type', 'checkbox');
     tAttrs.$set('role', tAttrs.type);
 
-    // Attach a click handler in compile in order to immediately stop propagation
-    // (especially for ng-click) when the checkbox is disabled.
-    tElement.on('click', function(event) {
-      if (this.hasAttribute('disabled')) {
-        event.stopImmediatePropagation();
-      }
-    });
-
-    // Redirect focus events to the root element, because IE11 is always focusing the container element instead
-    // of the md-checkbox element. This causes issues when using ngModelOptions: `updateOnBlur`
-    container.on('focus', function() {
-      tElement.focus();
-    });
+    return  {
+      pre: function(scope, element) {
+        // Attach a click handler during preLink, in order to immediately stop propagation
+        // (especially for ng-click) when the checkbox is disabled.
+        element.on('click', function(e) {
+          if (this.hasAttribute('disabled')) {
+            e.stopImmediatePropagation();
+          }
+        });
+      },
+      post: postLink
+    };
 
-    return function postLink(scope, element, attr, ngModelCtrl) {
+    function postLink(scope, element, attr, ngModelCtrl) {
       var isIndeterminate;
       ngModelCtrl = ngModelCtrl || $mdUtil.fakeNgModel();
       $mdTheming(element);
-      if (mdIndeterminateStateEnabled) {
+
+      // Redirect focus events to the root element, because IE11 is always focusing the container element instead
+      // of the md-checkbox element. This causes issues when using ngModelOptions: `updateOnBlur`
+      element.children().on('focus', function() {
+        element.focus();
+      });
+
+      if ($mdUtil.parseAttributeBoolean(attr.mdIndeterminate)) {
         setIndeterminateState();
         scope.$watch(attr.mdIndeterminate, setIndeterminateState);
       }
@@ -162,11 +164,7 @@ function MdCheckboxDirective(inputDirective, $mdAria, $mdConstant, $mdTheming, $
         var keyCode = ev.which || ev.keyCode;
         if (keyCode === $mdConstant.KEY_CODE.SPACE || keyCode === $mdConstant.KEY_CODE.ENTER) {
           ev.preventDefault();
-
-          if (!element.hasClass('md-focused')) {
-            element.addClass('md-focused');
-          }
-
+          element.addClass('md-focused');
           listener(ev);
         }
       }
@@ -182,17 +180,13 @@ function MdCheckboxDirective(inputDirective, $mdAria, $mdConstant, $mdTheming, $
           // Toggle the checkbox value...
           var viewValue = attr.ngChecked ? attr.checked : !ngModelCtrl.$viewValue;
 
-          ngModelCtrl.$setViewValue( viewValue, ev && ev.type);
+          ngModelCtrl.$setViewValue(viewValue, ev && ev.type);
           ngModelCtrl.$render();
         });
       }
 
       function render() {
-        if(ngModelCtrl.$viewValue && !isIndeterminate) {
-          element.addClass(CHECKED_CSS);
-        } else {
-          element.removeClass(CHECKED_CSS);
-        }
+        element.toggleClass('md-checked', ngModelCtrl.$viewValue && !isIndeterminate);
       }
 
       function setIndeterminateState(newValue) {

src/components/switch/switch.js

@@ -66,7 +66,7 @@ function MdSwitch(mdCheckboxDirective, $mdUtil, $mdConstant, $parse, $$rAF, $mdG
   };
 
   function mdSwitchCompile(element, attr) {
-    var checkboxLink = checkboxDirective.compile(element, attr);
+    var checkboxLink = checkboxDirective.compile(element, attr).post;
     // No transition on initial load.
     element.addClass('md-dragging');