What is meant by (0, somefunc)(args)

Question

I've been going through some of gmails javascript (writing an extension) and I've seen (0, _.ab)(a), or variations, all over the places. What does this achieve?

I've tried some tests such as

function a(a,b,c){ console.dir(a+b+c); }
(0, a)(1,2,3)

However I can't work out why they wouldn't just call a(1,2,3) directly. Does calling it using (0,a) have some odd benefit?

I've made a jsperf (http://jsperf.com/direct-vs-0-func-calls) to test this, and a(1) vs (0,a)(1) seem identical.

Edit: As Far as I can make out google only use it where they need to directly call a function, such as if ((0, _.wa)(a)) (taken from gmail's source)

That was what my thoughts were, but why would the minifier do that? — Joey Ciechanowicz, Jan 24 '14 at 14:37
@Pointy Wouldn't Closure Compiler (used on many Google products) just eliminate that code entirely? — Tibos, Jan 24 '14 at 14:38
Are you sure the first function isn't returning a function? It could be a chained call. — gpgekko, Jan 24 '14 at 14:39
@Tibos I would certainly expect it to, but then again I know precisely nothing about how it works :) — Pointy, Jan 24 '14 at 14:39
When you have jQuery, this works too: `(0, $)('body');`, it's basically the same as just calling `$('body');`... Wut. — Cerbrus, Jan 24 '14 at 14:42
@Cerbrus And this is surprising, because `$` isn't a function. — Zirak, Jan 24 '14 at 14:43

score 11 · Accepted Answer · answered Jan 24 '14 at 14:44

11

The (0, func)() syntax ensures that the context (this) in the called function func is the global context.

For example:

var myContext = {
    func: function () { 
        console.log(this);
    }
};

myContext.func();        // => myContext
(0, myContext.func)();   // => window

answered Jan 24 '14 at 14:44

Alon Gubkin

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Interesting. Is there some documentation on this, somewhere? – Cerbrus Jan 24 '14 at 14:45
Ahh, eliminating the scope chain to access global objects? Clever. – Ian Brindley Jan 24 '14 at 14:50
... the "comma operator". I always forget those are also operators. – Cerbrus Jan 24 '14 at 15:03

What is meant by (0, somefunc)(args)

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