How to concatenate var names in javascript?

Question

How can i concatenate var names to declare new vars in javascript?:

var foo = 'var';
var bar = 'Name';

How can i declare variable varName?

Just out of curiosity, why would you need to do that? Chances are, you're doing something wrong. — Sasha Chedygov, May 28 '09 at 03:06
It make Javascript harder to read because you can't search where declare variable by using simple search like this("var [variable name]"). — , May 28 '09 at 03:35
I have pre-declared var names that the user might be invoke based on user text input. — Babiker, May 28 '09 at 03:40

score 12 · Accepted Answer · answered May 28 '09 at 03:05

12

Try something like:

window[foo + bar] = "whatever"; 
alert(varName);

do not use the eval function unless you are absolutely certain about what's going in. window[] is much safer if all you're doing is variable access

answered May 28 '09 at 03:05

Jonathan Fingland

1

An additional reason to not use eval is that strict mode ECMAScript 5 does not allow eval to inject new variables – olliej May 28 '09 at 05:18

score 1 · Answer 2 · edited Jun 10 '13 at 21:04

1

WARNING: VaporCode! Off the top of my head...

window[foo + bar] = "contents of variable varName";

Does that work?

edited Jun 10 '13 at 21:04

Nathaniel Ford

answered May 28 '09 at 03:02

Daniel Magliola

score 1 · Answer 3 · edited May 23 '17 at 12:19

To dynamically declare a local variable (i.e. var fooName), I guess you could use eval:

eval('var ' + foo + bar);

Best to avoid eval though, if you can avoid it (see related question).

A better way is to set an object property. Defining a global variable is equivalent to setting a property on the global object window:

window[foo+bar] = 'someVal';

You can substitute window for another object if appropriate.

score 0 · Answer 4 · answered May 28 '09 at 04:36

0

Locally:

this[foo+bar] = true;

Globally:

window[foo+bar] = true;

answered May 28 '09 at 04:36

Karl Guertin

score -3 · Answer 5 · edited Aug 29 '12 at 14:53

-3

there may be a better way but eval should do it

eval('var ' + foo + bar);

edited Aug 29 '12 at 14:53

JMax

answered May 28 '09 at 03:03

SpliFF

2

@Babiker: Eval really is a bad practice, and dangerous, especially considering your comment about using user input to define what variable you'll be using. Not that anything a user can do in JS can be dangerous if your server is secure anyway, but still... using window[foo+bar] is definitely safer. – Daniel Magliola May 28 '09 at 03:47

5 Answers5