why is this referring to window object?

Question

   var x = 5,
    o = {
        x: 10,
        doIt: function doIt(){
            var x = 20;
            setTimeout(function(){
                alert(this.x);
            }, 10);
        }
    };
o.doIt();

Why is this referring to window object rather than o. I am inside the object o context, so it should print me 10 right?

It is referring to `window` is because it is inside `function(){}`. — Derek 朕會功夫, Dec 31 '12 at 08:03

score 4 · Answer 1 · edited May 23 '17 at 12:04

4

The anonymous function is executed after 10ms, and the execution context is not in o at that time.

Check out the answers to How do JavaScript closures work?

edited May 23 '17 at 12:04

Community

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1

answered Dec 31 '12 at 07:52

Osiris

4,127
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50

score 0 · Answer 2 · answered Dec 31 '12 at 07:54

0

To make this alert 20, change this.x to simply x.

answered Dec 31 '12 at 07:54

Evan Hahn

11,058
7
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1

PS: To make it alert 10, `o.x`. – Derek 朕會功夫 Dec 31 '12 at 08:01

score 0 · Accepted Answer · answered Dec 31 '12 at 08:02

var x = 5,
    o = {
        x: 10,
        doIt: function doIt(){
            var x = 20;
            setTimeout(function(){
                alert(this.x);
            }, 10);
        }
    };
o.doIt();

All functions passed into setTimeout() are executed in the global scope. The value is 5 because this.x is the same as window.x

why is this referring to window object?

3 Answers3