Question

I have a problem with Javascript forcing the [object DOMWindow] into an function I have in an object’s prototype. The full error I get is below:

Uncaught TypeError: Object [object DOMWindow] has no method 'positionconvert'

Basically what I’m doing is inside the object prototype under certain conditions I’m creating a var interval that counts off with window.setInterval():

var interval = window.setInterval(this.alertanimate, 500);

the alertanimate function is inside the same prototype, and uses the this variable in this line:

this.positionconvert(this.alerticon, -69, 55);

(positionconvert is yet another function, and alerticon is an object). The problem is when I get window.setInterval involved js starts assuming this is the DOM and not the object prototype, like I intended, presenting the above error. When I hard-code this to work with a specific object it works, but somewhere in this variable-passing the this variable loses its connection to the object. I hope this all makes sense? What am I doing wrong?

Answer 1

Passing this.alertanimate to setIntervall loses the connection to the main object. What this refers to in a function is entirely defined by how the function is called.
If you pass a function to setTimeout then this will refer to window.

You can do:

var self = this;

window.setInterval(function() {
    self.alertanimate();
}, 500);

In newer browsers, you can also use .bind() ^[MDN] (see docs for an alternative implementation):

window.setInterval(this.alertanimate.bind(this), 500);