apply function in JavaScript

Question

I'm learning JavaScript and I'm currently trying to figure out why (in Spidermonkey)

[].concat.apply([1], [[2]])

returns the expected [1, 2], but

Array.concat.apply([1], [[2]])

returns [2] instead of [1, 2].

Could someone provide a good explanation?

What does `Array.prototype.concat.apply([1], [[2]])` return? — Pointy, Dec 29 '11 at 15:16
Which browser are you using? `Array.concat` does not exist in Chrome. — Felix Kling, Dec 29 '11 at 15:16
Firefox has a "concat()" on the Array prototype (but not on the Array constructor object). — Pointy, Dec 29 '11 at 15:17
strange it allows you to run the second statement, it should be `(new Array).concat.apply([1], [[2]])` witch should return the expected result — Poelinca Dorin, Dec 29 '11 at 15:18

score 8 · Accepted Answer · answered Dec 29 '11 at 15:17

8

[].concat is Array.prototype.concat.

Array.concat is a Firefox-only static method that concatenates one or more arrays and ignores its this argument.

answered Dec 29 '11 at 15:17

SLaks

1

This has to be the answer but curiously MDN doesn't document that method :-) – Pointy Dec 29 '11 at 15:22
Which style is preferred, `[].concat` or `Array.prototype.concat`? – eljenso Dec 29 '11 at 15:27
@eljenso: `[]` is shorter, but it creates an extra array instance. `Array.prototype` is longer but faster. Your pick. – SLaks Dec 29 '11 at 15:29

1 Answers1