How do I update a variable from javascript setInterval?

Question

Say I have an object:

var myObj = function {
this.count = 0;
}

myObj.prototype {
   setCount : function() {
       var interval = setInterval(function() {
           this.count++;
       }, 500);
   }
}

The issue is count is always undefined within the setInterval so i can never increment the count variable within myObj to be something other than 0.

Quentin · Accepted Answer · 2012-07-16 13:29:02Z

4

this changes depending on the function being called (and how it said function is called).

The anonymous function you pass to setInterval is a different function.

Copy the value to a non-magic variable first.

   setCount : function() {
       var that = this;
       var interval = setInterval(function() {
           that.count++;
       }, 500);

See the this problem in the documentation.

answered Jul 16, 2012 at 13:29

Quentin

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1 Comment

Yoshi Over a year ago

or use bind

Dan O · Accepted Answer · 2012-07-16 13:30:26Z

0

setInterval() runs in the scope of the browser window, so this.count refers to window.count which does not exist.

answered Jul 16, 2012 at 13:30

Dan O

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1 Comment

Rolando Over a year ago

How to grab a reference to the actual count I want and then increment it with setInterval? Or is there some other means besides setInterval?

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