访问 javascript 中的 function 内的实例变量？

Question

How can I in the easiest way access an instance variable inside a function?

function MyObject(){

     //Instance variables
     this.handler;

     //Methods
     this.enableHandler = function(){
         var button = document.getElementById('button');
         button.onclick = function(){
             this.handler();//Is not working
         }
     }

}
var myObject = new MyObject();
myObject.handler = function(){
    alert('Hello World!');
}
myObject.enableHandler();

Note that I can set button.onclick = this.handler; . This is just an example. The main question is how I can access this.handler inside that function?

I can also define a new variable var handler = this.handler to access this.handler . But If a change handler will this.handler also be changes?

Answer 1

function MyObject(){

     //Instance variables
     this.handler;
     var that = this;  //notice change
     //Methods
     this.enableHandler = function(){
         var button = document.getElementById('button');
         button.onclick = function(){
             that.handler();//Is not working  notice the change
         }
     }

}
var myObject = new MyObject();
myObject.handler = function(){
    alert('Hello World!');
}
myObject.enableHandler();

If you assign this to a var within the scope of the outer function, it is passed to the inner functions scope chain. Within your inner function referencing this refers to the inner function, referencing the variable you assigned this, in our case "that", refers back to that object.