Why does Javascript's OR return a value other than true/false?

Posted by Fletcher Moore on Stack Overflow See other posts from Stack Overflow or by Fletcher Moore
Published on 2010-06-03T13:35:56Z Indexed on 2010/06/03 13:44 UTC
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JavaScript

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syntax

I saw this construction in order to get the browser viewport width:

function () { return window.innerWidth || document.documentElement.clientWidth || document.body.clientWidth; }

I understand the browser quirks involved. What I don't understand is why || returns the value. So I tried this alert(undefined || 0 || 3); and sure enough, it alerts 3. I find this bizarre, because I expect true or false. Could anyone explain what's going on?

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