Question

Code:

​var a = function() {
   this.message = "hello";
    this.shout = function(){
        alert(this.message); // alerted undefined
    }
    this.Timer = setTimeout(this.shout, 3000);
}

var b = new a();

I get undefined in the alert dialog. I’ve tried “this.shout()” in setTimeout but then there is a DOM error on finding shout. How do I deal with this?

Answer 1

this in your function shout refers to the function shout, rather than the function a

If you define your variable in the scope of a instead of using this, you can refer to it later on and get it’s value:

var a = function() {
    var message = "hello";
    this.shout = function(){
        alert(message); // Alerts hello
    }
    this.Timer = setTimeout(this.shout, 3000);
}

var b = new a();

Or if you’d like you can store a reference instead, so that you can use self to refer to a:

var a = function() {
    this.message = "hello";
    var self = this;

    this.shout = function(){
        alert(self.message); // Alerts hello
    }
    this.Timer = setTimeout(this.shout, 3000);
}

var b = new a();