Two pipe symbols (OR) in this Javascript line

Question

Possible Duplicate:
What does “options = options || {}” mean in Javascript?

I have seen this in JS:

item = item || {};

I'm guessing it's some variation of a ternary operator but what does is actually do?

Are we getting some Javascript snobbs in the house tonight downvoting or just general silly people!? — benhowdle89, Apr 27 '12 at 22:48
@Martin. and what would you suggest I could have searched to receive this answer... — benhowdle89, Apr 27 '12 at 22:49
good question. I have been searching for a while and finally [got it](http://stackoverflow.com/questions/9579262/logical-operator-in-javascript-0-stands-for-boolean-false). But to be honest, it isn't as easy as I thought. Reverting all my downvotes — Martin., Apr 27 '12 at 22:58
@Martin. Thank you. As a self taught developer, believe me, if I could have Googled it...I would have. — benhowdle89, Apr 27 '12 at 23:00
@ben yep, I've had a discussion about this on meta (now lost). Yep, it is really hard to search for such operators. — Martin., Apr 27 '12 at 23:04
@Martin, may be it's been answered million times but these answers are not wrong in context and it's wrong to down vote a right answer. Well, you mentioned cwolves that why he didn't voted it to close the answer but my question is why you didn't voted to close the question ? — The Alpha, Apr 27 '12 at 23:04
@Martin. I understand but none deserve a down vote for a poor answer unless it's wrong, you may don't up vote it and could have made a comment. — The Alpha, Apr 27 '12 at 23:08
But finally you removed your down votes, that's a good thing. :-) — The Alpha, Apr 27 '12 at 23:11
@SheikhHeera two of them are wrong, they words like `if item exist` or `if item is not defined`, this is wrong since they don't cover all possibilities. But he still did wrong because he dv because other reasons — ajax333221, Apr 27 '12 at 23:36
After all, I got downvoted into oblivion - just as I expected :) — Martin., Apr 27 '12 at 23:50
@Martin. I try not to get too worked up over imaginary internet points. — arkon, Aug 06 '16 at 07:05

ajax333221 · Accepted Answer · 2012-04-27T23:17:20.017

38

(expr1 || expr2)

"Returns expr1 if it can be converted to true; otherwise, returns expr2."

source

So when expr1 is (or evaluates to) one of these 0,"",false,null,undefined,NaN, then expr2 is returned, otherwise expr1 is returned

edited Apr 27 '12 at 23:17

answered Apr 27 '12 at 23:03

ajax333221

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Niet the Dark Absol · Answer 2 · 2012-04-28T02:19:05.013

12

It's called redundancy, but in this case it's a good thing. Basically, if item is not defined (or otherwise falsy (false, 0, ""...), then we give it a default value.

Most common example is in events:

evt = evt || window.event;

edited Apr 28 '12 at 02:19

answered Apr 27 '12 at 22:44

Niet the Dark Absol

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score 8 · Answer 3 · edited Apr 27 '12 at 22:45

8

If item exists, set item to item, or set it to {}

edited Apr 27 '12 at 22:45

Martin.

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answered Apr 27 '12 at 22:44

Dhaivat Pandya

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you don't deserve a down vote. – The Alpha Apr 27 '12 at 23:05
@Sheikh yeah, the answer isn't wrong, but it's pretty poor I think. Kolink and ajax have the best answers here. Especially Kolink deserves the upvote – Martin. Apr 27 '12 at 23:06

score 2 · Answer 4 · edited Apr 27 '12 at 22:58

2

It equates to:

if( !item ){ item = {}; }

edited Apr 27 '12 at 22:58

Martin.

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answered Apr 27 '12 at 22:44

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So if item is FALSE then item is an empty object? – benhowdle89 Apr 27 '12 at 22:44
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`false` or `undefined` or any other falsey value, yes – Apr 27 '12 at 22:45
This question has been answered million times, plus this answer is quite poor – Martin. Apr 27 '12 at 22:46
1

The question, maybe. Nothing wrong with my answer. – Apr 27 '12 at 22:46
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@cwolves you're >10k, you should vote to close the question instead. It is EXACT duplicate – Martin. Apr 27 '12 at 22:47

Two pipe symbols (OR) in this Javascript line

4 Answers4

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