How to send array to function as multiple arguments?

Question

In Javascript I have simple test code:

function x(a, b) {
  alert(a);
  alert(b);
}

var c = [1,2];
x(c);

which send an argument c to function x() as one argument, assigned to a and b stays undefined :-/

How can I send an array as multiple arguments to a function, not as one array?

Why are you wrapping them in an array in the first place if you don't want an array? Just do x(1,2) — TheZ
– TheZ, Commented Jul 17, 2012 at 23:38
@JuanMendes Alright, then maybe x(c[0],c[1])? I guess I just don't understand what is required. — TheZ
– TheZ, Commented Jul 17, 2012 at 23:40
@TheZ Usually, because you don't know how many arguments you need to pass. That's why Function.apply exists — Ruan Mendes
– Ruan Mendes, Commented Jul 17, 2012 at 23:41
@JuanMendes Oh I see! I guess since the problem said nothing about variable sized arrays I didn't get that at all. Thanks — TheZ
– TheZ, Commented Jul 17, 2012 at 23:43

Andrew Whitaker · Accepted Answer · 2012-07-17 23:51:09Z

24

Check out apply.

In your case (since you aren't using this in the function), you can simply pass window (or this) as the "this" argument:

x.apply(this, [1, 2]);

Example: http://jsfiddle.net/MXNbK/2/

Per your question about passing null as the "this" argument, see MDN's comment in the linked article on the "this" argument:

Note that this may not be the actual value seen by the method: if the method is a function in non-strict mode code, null and undefined will be replaced with the global object, and primitive values will be boxed.

edited Jul 17, 2012 at 23:51

answered Jul 17, 2012 at 23:37

Andrew Whitaker

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7 Comments

Ωmega Over a year ago

Would not be nicer to pass null as the first argument, as this has nothing related to such function(ality)...?

Andrew Whitaker Over a year ago

You could, but I believe this will still be window inside of the function.

Ruan Mendes Over a year ago

@Ωmega Some browsers break when you pass null as this, even if not used

Ωmega Over a year ago

@JuanMendes - Ooops, really? I believe they should not, but okay... How about zero 0 - would that be acceptable for all browsers?

Andrew Whitaker Over a year ago

@Ωmega 0 wouldn't hurt, but why not just pass this? What is the advantage to passing anything else?

|

Lukáš Voda · Accepted Answer · 2015-11-11 19:56:59Z

24

Or, in browsers with ECMAScript 2015 (or with Babel transpiler), you can use the new spread operator:

x(...[1, 2])

answered Nov 11, 2015 at 19:56

Lukáš Voda

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2 Comments

Andreas Louv Over a year ago

This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post. - From Review

Mike Cluck Over a year ago

@dev-null This is a valid answer to the question. In ES6 the spread operator works very much like Function.apply.

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