Copying array onto the "this" variable (creating an Array-like object)

Question

Is there a better way to copy an array onto the this variable

function obj(arr) {
  for (var i=0, l=arr.length; i<l; ++i) {
    this[i] = arr[i];
  }
  this.length = arr.length;
}

var o = new obj([1,2,3,4]);
console.log(o[0]); // Outputs 1

Is there any other way to do it, instead of iterating over the whole arr ?

You can refer following [post](http://stackoverflow.com/questions/7486085/copying-array-by-value-in-javascript) — Rajesh, Nov 11 '15 at 17:26
@Rajesh the post you mentioned has nothing to do with my question — Dano, Nov 11 '15 at 17:27
Dano the answer below is good. But I don't imagine why you need this. It's weird and dangerous. — Marcos Pérez Gude, Nov 11 '15 at 17:29

Felix Kling · Accepted Answer · 2015-11-11T17:55:17.830

2

You can use Array#push this way:

function obj(arr) {
  Array.prototype.push.apply(this, arr);
}

This will treat this like an array, adding all the elements from arr and setting length correctly. See also Function#apply.

But of course there is still an internal loop. You cannot copy / move a collection values to another collection without iterating over it (unless, I guess, the collections use structural sharing)

edited Nov 11 '15 at 17:55

answered Nov 11 '15 at 17:46

Felix Kling

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score 1 · Answer 2 · answered Nov 11 '15 at 17:27

1

You could do it like this:

function obj() {
    return this;
}

var o = obj.apply([1,2,3,4]);
console.log(o[0]); // Outputs 1

answered Nov 11 '15 at 17:27

dave

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Are you aware that this simply returns the array itselft? is this a joke? – Felix Kling Nov 11 '15 at 17:43
This doesn't do any *copying* which was clearly listed as a requirement. – Mike Christensen Nov 11 '15 at 17:49

Copying array onto the "this" variable (creating an Array-like object)

2 Answers2