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Message-ID: <7998487.AcjmSas2GF@PointedEars.de>
From: Thomas 'PointedEars' Lahn <PointedEars@web.de>
Reply-To: Thomas 'PointedEars' Lahn <cljs@PointedEars.de>
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Date: Tue, 28 Jan 2014 15:58:34 +0100
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Subject: Re: I thought I understood JavaScript till they asked me this on a job interview
Newsgroups: comp.lang.javascript
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Xref: csiph.com comp.lang.javascript:22841

Alon Melanker wrote:

>   function damn() {
>       this.x = 4;
>       var y = 3;
>       
>       setTimeout(function() {alert(this.x); alert(y)}, 100);
>       
>        this.aa = function() {
>         alert(this.x);
>       };
>   }
>   
>   aaa = new damn();
>   aaa.aa();
> 
> What would be the output?!
> 
> The correct answer should be 4 undefined and 3.

Yes, although there is a race condition and it could be “undefined”, “3”, 
and “4” as well.  Or a SyntaxError or TypeError exception could be thrown.

> I answered 4 4 3.
> 
> The question is why this.x inside setTimeout does not alert 4?

I could tell you (and probably others will, with wrong explanations
in-between), but try debugging first.  You will learn more for your next 
interview this way.

<http://devtoolsecrets.com/>
<http://PointedEars.de/faq#posting>

-- 
PointedEars

Twitter: @PointedEars2
Please do not Cc: me. / Bitte keine Kopien per E-Mail.