Javascript「this」scope

Question

我在寫一些JavaScript代碼。我對這個關鍵詞有點困惑。如何訪問dataReceivedHandler函數中的記錄器變量？

MyClass: { 
    logger: null, 
    init: function() { 
     logger = LogFactory.getLogger(); 
    }, 
    loadData: function() { 
     var dataReceivedHandler = function() { 
      // how to access the logger variable here? 
     } 

     // more stuff 
    } 
}; 

Answer 1

假設loadData被稱爲像這樣：

MyClass.loadData(); 

則：

loadData: function() { 
    var self = this; 
    var dataReceivedHandler = function() { 
     self.logger ... 
    } 

    // more stuff 
} 

Answer 2

你可以這樣做的loadData函數裏面的東西訪問你的對象......

MyClass: { 
    logger: null, 
    init: function() { 
     this.logger = LogFactory.getLogger(); 
    }, 
    loadData: function() { 
     var self = this; 
     var dataReceivedHandler = function() { 
      // how to access the logger variable here? 
      self.logger.log('something'); 
     } 

     // more stuff 
    } 
}; 

Answer 3

Becaus e dataReceivedHandler是一個匿名函數，this將引用全局作用域上的窗口對象。我想你可以繞過這兩條路。

一）內部loadData創建一個變量來保存它的上下文然後用它裏面dataReceivedHandler這樣：

loadData: function() { 
    var self = this; 
    var dataReceivedHandler = function() { 
     console.log(self.logger); 
    } 

    // more stuff 
} 

b）使用apply或call更改匿名函數的上下文。

loadData: function() { 
    var dataReceivedHandler = function() { 
     console.log(this.logger); 
    } 
    // more stuff 
    dataReceivedHandler.call(this); // by passing this as the first argument we make sure the context of the excuted function is our current scope's this 
} 

由於性能和內存使用優化，我更喜歡選項B，但兩者都可以正常工作。