Finbarr Finbarr - 1 year ago 91
Javascript Question

Use dynamic variable names in JavaScript

In PHP you can do amazing/horrendous things like this:

$a = 1;
$b = 2;
$c = 3;
$name = 'a';
echo $$name;
// prints 1

Is there any way of doing something like this with Javascript?

E.g. if I have a
var name = 'the name of the variable';
can I get a reference to the variable with name

Answer Source

Since ECMA-/Javascript is all about Objects and Contexts (which, are also somekind of Object), every variable is stored in a such called Variable- (or in case of a Function, Activation Object).

So if you create variables like this:

var a = 1,
    b = 2,
    c = 3;

In the Global scope (= NO function context), you implicitly write those variables into the Global object (= window in a browser).

Those can get accessed by using the "dot" or "bracket" notation:

var name = window.a;


var name = window['a'];

This only works for the global object in this particular instance, because the Variable Object of the Global Object is the window object itself. Within the Context of a function, you don't have direct access to the Activation Object. For instance:

function foobar() {
   this.a = 1;
   this.b = 2;

   var name = window['a']; // === undefined
   name = this['a']; // === 1

new foobar();

new creates a new instance of a self-defined object (context). Without new the scope of the function would be also global (=window). This example would alert undefined and 1 respectively. If we would replace this.a = 1; this.b = 2 with:

var a = 1,
    b = 2;

Both alert outputs would be undefined. In that scenario, the variables a and b would get stored in the Activation Object from foobar, which we cannot access (of course we could access those directly by calling a and b).