Access instance variable inside a function in javascript?

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.handlerto access this.handler. But If a change handlerwill this.handler also be changes?

You mentioned jQuery but I don't see you using it...

Felix Kling
– Felix Kling

2011-06-30 17:39:23 +00:00
Commented Jun 30, 2011 at 17:39 — Felix Kling
– Felix Kling, Commented Jun 30, 2011 at 17:39

Kevin Bowersox · Accepted Answer · 2011-06-30 17:06:14Z

10

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.

answered Jun 30, 2011 at 17:06

Kevin Bowersox

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2 Comments

einstein Over a year ago

Ok if I change that.handler will this.handler also be changed?

Kevin Bowersox Over a year ago

yes but you also need to do the var that = this; assignment, look at the two places i put notice change in the comments.

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