Use dynamic variable names in JavaScript

Question

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 name?

Answer 1

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; 

or

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    alert(name);    name = this['a']; // === 1    alert(name); }  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).

Answer 2

eval is one option.

var a = 1; var name = 'a';  document.write(eval(name)); // 1 

Warning: Note that using the eval() function is not recommended if you don't know what you are doing, since it brings multiple security issues. Use something else unless absolutely necessary. See the MDN page for eval for more info.