AngularJS前缀$和$$如何使用？

• $：

  AngularJs中的$是一个内置对象，它包含应用程序数据和方法。

  scope($)充当控制器和视图之间的链接。

  

  范围($)

  在控制器函数内部，可以附加scope($)的属性和方法。可以使用Expression ， ng-model或ng-bind指令在视图中显示范围数据。

      
      
  
  
  $scope
      
          Message: 
          {{message}}
           
           
      
      
          var ngApp = angular.module('Ng', []);
    
          ngApp.controller('myController', function ($scope) {
              $scope.message = "GFG!";        
          });
      

  输出：
  

  范例2：

      
    
      
          
              First Name: 
              Middle Name: 
              Last Name: 
              
           Full Name: {{firstName +middleName+ " " + lastName}}
          
    
          
              var app = angular.module("myApp", []);
              app.controller("myCtrl", function ($scope) {
                  $scope.firstName = "Geeks";
                  $scope.middleName = "for";
                  $scope.lastName = "Geeks";
              });
          
      

  输出：
  

  $ rootScope：

  AngularJS应用程序由单个$ rootScope组成。其他所有$ scope都是子对象。$ rootscope具有附加的属性和方法，将对所有控制器可用。

  Method	Description
  $new	It is used to create new Child Scope
  $watch	It is used to Register a callback which is to be executed whenever the model property changes.
  $watchGroup	It is used to register a callback  which is to be executed whenever model properties changes. We specify an array of properties in this.
  $watchCollection	It is used to register a callback which is to be executed whenever model object or array property changes.
  $digest	It processes all of the watchers of the current scope and its children.
  $destroy	Remove the current scope from parent scope.
  $eval	Execute expressions on the current scope.
  $emit	It is used to dispatch the specified event upwards till $rootScope.
  $broadcast	It is used to dispatch the specified event downwards till child Scope.

  范例3：

      
     
  
  
   $watch 
      
          Enter Message:  
          New : {{newMessage}} 
          Old : {{oldMessage}} 
      
      
          var ngApp = angular.module('Ng', []);
        
          ngApp.controller('Controller', function ($scope) {
              $scope.message = "GFG!";
    
              $scope.$watch('message', function (newValue, oldValue) {
                  $scope.newMessage = newValue;
                  $scope.oldMessage = oldValue;
              });
          });
      

  输出：
  

• $$

  其中的$$被视为私有变量。我们使用$$来避免内部变量冲突，并且不暴露给外部使用。

  下面列出了其中一些：

  $$观察者，$ watchers，$ childHead，$ childTail，$ ChildScope等。

  Method	Description
  $$watchers	It contains all of the watches associated with the scope
  $$asyncQueue	It is a async task queue.It is consumed on every digest
  $$postDigest(fn)	It executes fn after the next digest cycle.
  $$destroyed	It destroys the scope.

  句法：

  $$('.selector');

  或者

  element.all(by.css('.selector'));

  借助AngularJS核心功能，应用程序模块之间的常见通信方式是使用$ parent，$ childHead，$ nextSibling建立控制器之间的连接。

  例子：

      
    
      
          
              First Name: 
              Middle Name: 
              Last Name: 
              
         Full Name: {{firstName +middleName+ " " + lastName}}
          
    
          
              var app = angular.module("myApp", []);
              app.controller("myCtrl", function ($scope) {
                  $$scope.firstName = "Geeks";
                  $$scope.middleName = "for";
                  $$scope.lastName = "Geeks";
              });
          
      

  输出：
  

  当我们添加$$时，将产生上述输出，因为它充当私有对象。

因此，为防止在编写代码时出现意外的名称冲突，请在公共对象前添加$角前缀，在$$之前添加私有对象。