feat(ngRoute): cancel $routeChangeStart via $event.preventDefault()

This change allows ngRoute route changes to be cancelled using $event.preventDefault.

This enables route changes to be aborted at the discretion of the application.

Route changes may not be cancelled if forceReload is set to true.

Closes angular#5581

src/ngRoute/route.js

@@ -375,11 +375,31 @@ function $RouteProvider(){
      * defined in `resolve` route property. Once  all of the dependencies are resolved
      * `$routeChangeSuccess` is fired.
      *
+     * The route change may be cancelled with angularEvent.preventDefault(), which will
+     * in turn trigger a {@link ngRoute.$route#events_$routeChangeCancelled $routeChangeCancelled}
+     * event.
+     *
      * @param {Object} angularEvent Synthetic event object.
      * @param {Route} next Future route information.
      * @param {Route} current Current route information.
      */
 
+    /**
+     * @ngdoc event
+     * @name ngRoute.$route#$routeChangeCancelled
+     * @eventOf ngRoute.$route
+     * @eventType broadcast on root scope
+     * @description
+     * Broadcasted after a route has been cancelled during
+     * {@link ngRoute.$route#events_$routeChangeStart $routeChangStart}, using the
+     * angularEvent.preventDefault() method. This method enables applications to prevent
+     * a route change from occurring without any additional work.
+     *
+     * @param {Object} angularEvent Synthetic event object.
+     * @param {Route} cancelled The cancelled route information.
+     * @param {Route} current Current route information.
+     */
+
     /**
      * @ngdoc event
      * @name ngRoute.$route#$routeChangeSuccess
@@ -494,8 +514,15 @@ function $RouteProvider(){
         angular.copy(last.params, $routeParams);
         $rootScope.$broadcast('$routeUpdate', last);
       } else if (next || last) {
+        var wasForceReload = forceReload;
         forceReload = false;
-        $rootScope.$broadcast('$routeChangeStart', next, last);
+
+        if ($rootScope.$broadcast('$routeChangeStart', next, last).defaultPrevented &&
+            !wasForceReload) {
+          $rootScope.$broadcast('$routeChangeCancelled', next, last);
+          return;
+        }
+
         $route.current = next;
         if (next) {
           if (next.redirectTo) {

test/ngRoute/routeSpec.js

@@ -723,6 +723,61 @@ describe('$route', function() {
         expect($exceptionHandler.errors).toEqual([myError]);
       });
     });
+
+
+    it('should broadcast $routeChangeCancelled if $routeChangeSuccess.defaultPrevented', function() {
+      module(function($routeProvider) {
+        $routeProvider.when('/r1', {
+          templateUrl: 'r1.html'
+        });
+      });
+      inject(function($route, $httpBackend, $location, $rootScope) {
+        var success = jasmine.createSpy('$routeChangeSuccess'),
+            error = jasmine.createSpy('$routeChangeError'),
+            cancelled = jasmine.createSpy('$routeChangeCancelled');
+        $rootScope.$on('$routeChangeStart', function($event) { $event.preventDefault(); });
+        $rootScope.$on('$routeChangeSuccess', success);
+        $rootScope.$on('$routeChangeError', error);
+        $rootScope.$on('$routeChangeCancelled', cancelled);          
+
+        $location.path('/r1');
+        $rootScope.$digest();
+
+        expect(success).not.toHaveBeenCalled();
+        expect(error).not.toHaveBeenCalled();
+        expect(cancelled).toHaveBeenCalled();
+      });
+    });
+
+
+    it('should not broadcast $routeChangeCancelled if force-reloading', function() {
+      module(function($routeProvider) {
+        $routeProvider.when('/r1', {
+          templateUrl: 'foo.html'
+        });
+      });
+      inject(function($route, $httpBackend, $location, $rootScope) {
+        var success = jasmine.createSpy('$routeChangeSuccess'),
+            error = jasmine.createSpy('$routeChangeError'),
+            cancelled = jasmine.createSpy('$routeChangeCancelled');
+
+        $location.path('/r1');
+        $rootScope.$digest();
+        $httpBackend.flush();
+
+        $rootScope.$on('$routeChangeStart', function($event) { $event.preventDefault(); });
+        $rootScope.$on('$routeChangeSuccess', success);
+        $rootScope.$on('$routeChangeError', error);
+        $rootScope.$on('$routeChangeCancelled', cancelled);          
+
+        $route.reload();
+        $rootScope.$digest();
+
+        expect(cancelled).not.toHaveBeenCalled();
+        expect(error).not.toHaveBeenCalled();
+        expect(success).toHaveBeenCalled();
+      });
+    });
   });