fix(ngIf): destroy child scope when destroying DOM

src/ng/directive/ngIf.js

@@ -87,23 +87,31 @@ var ngIfDirective = ['$animate', function($animate) {
     $$tlb: true,
     compile: function (element, attr, transclude) {
       return function ($scope, $element, $attr) {
-        var block = {}, childScope;
+        var block, childScope;
         $scope.$watch($attr.ngIf, function ngIfWatchAction(value) {
-          if (block.startNode) {
-            $animate.leave(getBlockElements(block));
-            block = {};
-          }
-          if (block.startNode) {
-            getBlockElements(block).$destroy();
-            block = {};
-          }
+
           if (toBoolean(value)) {
+
             childScope = $scope.$new();
             transclude(childScope, function (clone) {
-              block.startNode = clone[0];
-              block.endNode = clone[clone.length++] = document.createComment(' end ngIf: ' + $attr.ngIf + ' ');
+              block = {
+                startNode: clone[0],
+                endNode: clone[clone.length++] = document.createComment(' end ngIf: ' + $attr.ngIf + ' ')
+              };
               $animate.enter(clone, $element.parent(), $element);
             });
+
+          } else {
+
+            if (childScope) {
+              childScope.$destroy();
+              childScope = null;
+            }
+
+            if (block) {
+              $animate.leave(getBlockElements(block));
+              block = null;
+            }
           }
         });
       };

test/ng/directive/ngIfSpec.js

@@ -36,7 +36,7 @@ describe('ngIf', function () {
     expect(element.children().length).toBe(0);
   });
 
-  it('should create a new scope', function () {
+  it('should create a new scope every time the expression evaluates to true', function () {
     $scope.$apply('value = true');
     element.append($compile(
       '<div ng-if="value"><span ng-init="value=false"></span></div>'
@@ -45,6 +45,26 @@ describe('ngIf', function () {
     expect(element.children('div').length).toBe(1);
   });
 
+  it('should destroy the child scope every time the expression evaluates to false', function() {
+    $scope.value = true;
+    element.append($compile(
+        '<div ng-if="value"></div>'
+    )($scope));
+    $scope.$apply();
+
+    var childScope = element.children().scope();
+    var destroyed = false;
+
+    childScope.$on('$destroy', function() {
+      destroyed = true;
+    });
+
+    $scope.value = false;
+    $scope.$apply();
+
+    expect(destroyed).toBe(true);
+  });
+
   it('should play nice with other elements beside it', function () {
     $scope.values = [1, 2, 3, 4];
     element.append($compile(