Using a variable value to call an array element

Question

I have a string variable which contains the name of an array. What I'd like to do is access an element of that array. And write it to another variable. How can I do this?

var sample = new Array();
sample[0] = 'one';
sample[1] = 'two';

var arrayname = "sample";
var number = arrayname[1];  ///  Something like this, although I realize this doesn't work for obvious reasons...

I've read other questions in regards to using an variable value as a function, but I didn't understand the approach or even if this would work for the above situation.

Thanks in advance!!

See this: http://stackoverflow.com/questions/8588307/calling-a-jquery-function-named-in-a-variable/8588392#8588392 — Andreas Louv, Jan 12 '12 at 14:02

score 3 · Accepted Answer · answered Jan 12 '12 at 14:01

3

This should do it:

    var sample = new Array();
    sample[0] = 'one';
    sample[1] = 'two';

    var arrayname = "sample";
    var number = window[arrayname][1];
    alert(number);

answered Jan 12 '12 at 14:01

Skyrim

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5
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1

But only if you run it in window scope, not inside a function. – Steven de Salas Jan 12 '12 at 14:17
definitely...as far as I know, if you created a local variable within a function, there is no way to get it with just a string name. If a JS Super Guru can show me otherwise, I'd really like to know!! – Skyrim Jan 12 '12 at 14:28

Pointy · Answer 2 · 2012-01-12T14:05:40.803

There's no universal way in JavaScript to do exactly what you've got set up there, but you can use string variables to access object properties in a dynamic way.

var objArr = { array1: [], array2: [] };

Now you can use a variable with the value "array1" or "array2" to get at those arrays:

var name = "array2";
objArr[name].push(14);

What you cannot do in JavaScript is access local variables by a dynamic name, or indirectly if you prefer. You can access global variables that way if you have a name for the global context, which in a browser is the window object:

window[ name ].push(17);

However there's no way to get a similar name for a local scope.

edit — @Neal points out (and is downvoted mercilessly) that eval() can do what you want, but a lot of people recommend staying far away from eval() unless it's absolutely unavoidable (which is really rare). I've trained myself to ignore it so well that I always forget about it when questions like this are asked (which is, oddly, quite often on SO, though in my programming practice I never find myself wanting to do this).

Technically, eval should be able to do *exactly* what he wants but I perfectly understand why you wouldn't want to tell him that :) — hugomg, Jan 12 '12 at 14:03
@missingno as I said in my edit, I actually never think about `eval()` so I simply forgot :-) — Pointy, Jan 12 '12 at 14:08
@Pointy i even said in my post that it was **not** the best approach. I should have bolded it :-P — Naftali, Jan 12 '12 at 16:24

score 0 · Answer 3 · answered Jan 12 '12 at 14:01

0

You could use something like:

var arrayName = "sample",
    number = window[arrayname][1];

answered Jan 12 '12 at 14:01

jabclab

14,786
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score 0 · Answer 4 · answered Jan 12 '12 at 14:01

0

I mean you can use eval, but it is not the best approach:

eval("var arrayname = sample");
var number = arrayname[1];

Why not just do:

var arrayname = sample;
var number = arrayname[1];

answered Jan 12 '12 at 14:01

Naftali

144,921
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I don't like `eval()` any more than anybody else but this doesn't really deserve a downvote; it's technically correct :-) – Pointy Jan 12 '12 at 14:06

score 0 · Answer 5 · answered Jan 12 '12 at 14:03

0

If it's in the global scope, you can access your array by doing

var sample = new Array();
sample[0] = 'one';
sample[1] = 'two';
var arrayname = "sample";
var number = (window[arrayname])[1]

answered Jan 12 '12 at 14:03

Grooveek

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score 0 · Answer 6 · answered Jan 12 '12 at 14:04

0

var sample = new Array();
sample[0] = 'one';
sample[1] = 'two';
var obj = {"sample": sample}

var arrayname = "sample";
var number = obj[arrayname][1];

answered Jan 12 '12 at 14:04

itea

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score 0 · Answer 7 · answered Jan 12 '12 at 14:04

Out of my head...

First declare some global variable

var buf;

Then

var sample = new Array();
sample[0] = 'one';
sample[1] = 'two';

var arrayname = "sample";
eval('buf=' + arrayname + ';');
var number = buf[1];

Damn undesirable way but does what you want...

Using a variable value to call an array element

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