Use argument as variable name (Javascript)

Question

I can't seem to find a question that answers this directly.

I'd like to use a function argument as the name of a variable within that function.

e.g.,

test(var1);
function test(foo)
{
 var foo = 'Hello world!'; // Set var1
}
alert(var1); // Hello world!

Can I use the brackets here (i.e., window.[ ])?

• Drixson Oseña: you mean your variable contains a bracket? or you mean array?
• user2246674: Don't think in terms of variables. Think of terms in properties (and how they relate to Maps/Dictionaries/Objects) - properties can have arbitrary string names and can accessed as obj[propNameExpression]. Then consider that window evaluates to an Object and thus supports properties and normal property access (although some DOM/browser properties are "reserved"). That being said, using window[prop], for an unconstrained prop value, is probably questionable. Consider myObject[prop] instead. You'll also need to pass in "var1" as a string value (or the identifier will be evaluated).

Answer 1

Yeah, you can use brackets:

window[foo] = "Hello World"

Here's a JSFiddle

Answer 2

Er...okay, so this is almost certainly not a good idea.

Short answer: sorta. If you're running in a browser, you can do this:

var polluteGlobalNamespace = function(symbol) {
 window[symbol] = "whatever";
};
polluteGlobalNamespace('foo');
console.log(foo);

But that only works for global variables. There is no way to do this with function-scoped variables, because JavaScript lacks first class environments.

But unless you're doing some deep dark metaprogramming, this isn't a good idea. It might be better to post the problem that you're trying to solve with this function to see what the idiomatic way to do it is.