javascript - 为什么 $httpbackend.flush 会导致我的 $scope.$watch 无限期触发？

Question

为 Angular 控制器运行 Jasmine 单元测试时，它会失败并显示消息

'Error: 10 $digest() iterations reached. Aborting!'  

当 $httpbackend.flush() 被调用时。

这是我的控制器：

theApp.controller("myCtrl", function($scope, $http, globalstate){
     $scope.currentThing = globalstate.getCurrentThing();
         $scope.success = false;

     $scope.$watch(globalstate.getCurrentThing, function(newValue, oldValue){
          $scope.currentThing = newValue;
     });

     $scope.submitStuff = function(thing){
          $http.put('/api/thing/PutThing', thing, {params: {id: thing.Id}})
          .success(function(){          
                $scope.success = true;
          })
     };
});

这是我的单元测试：

describe('myCtrl', function(){

    var myController = null;
    beforeEach(angular.mock.module('theApp'));

    beforeEach(inject(function($injector){
        $rootScope = $injector.get('$rootScope');
        scope = $rootScope.$new();

        $httpBackend = $injector.get('$httpBackend');

        $controllerService = $injector.get('$controller');
        mockGlobalState = {
            getCurrentThing : function(){
                return {Id: 1, name: 'thing1'};
            }
        };

        $controllerService('myCtrl', {$scope: scope, globalstate: mockGlobalState});
   }));

   it('should set flag on success', function(){
       var theThing = {Id: 2, name: ""};
       $httpBackend.expectPUT('/api/thing/PutThing?id=2',JSON.stringify(theThing)).respond(200,'');

       scope.submitStuff(theThing, 0);

       $httpBackend.flush();

       expect(scope.basicupdateSucceeded).toBe(true);
   });

});

当我将 $scope.$watch 中的第三个参数设置为 true（比较对象相等性而不是引用）时，测试通过了。

为什么 $httpbackend.flush() 会导致 $watch 触发？为什么手表在那之后会自行触发？

Answer 1

// **when you are assigning something to currentThing, it will trigger watch**
$scope.currentThing = globalstate.getCurrentThing();
$scope.success = false;

$scope.$watch(globalstate.getCurrentThing, function(newValue, oldValue){
    // **here you are changing the item to whom you are watching so it can cause recursion.**
    $scope.currentThing = newValue;
});