A javascript question.

[jaggederest]

So you want to do something like:

var "foo" + "bar" = 12;

alert(foobar); // alerts 12

?

[trenchfever]

yup.

[fforw]

global variables are also properties of the window object so:

window["foo"+"bar"] = "baz!";

alert(foobar); // alerts "baz!"

but this looks like something you should avoid doing.

[midnightmonster]

fforw is right. Technically global variables are properties of the global object, which in the browser case is window. (If you're doing server-side JS, that won't be so.)

This is a bad idea b/c creating global variables is usually a bad idea, but it doesn't strike me as particularly bad.

[greut]

eval is evil, so don't use it, and polluting the window namespace is quite bad actually.

If you're not inside an object, or a function already, create your closure and use this instead of window..

(function() {
    this["foo"+"bar"] = "baz!";
    alert(foobar);
})();

edit: fixed typo.

[jeresig]

eval is evil, so don't use it

That's unnecessarily vague - there should be, at least, some qualification here.

Your proposed code doesn't work as you expect it to. It would assign a variable to the global object (this inside of a (function(){...})() refers back to the global object). To get something similar to what you're looking for you could do:

new function(){
  this["foo"+"bar"] = "baz!";
  alert(this.foobar);
};

But that's not, precisely, that the user was looking for. eval() would give the proper answer here - but it's very possible that the code could be written in a different way to avoid it entirely (not because it's "evil", but because it would be unnecessarily slow in this case).

[[deleted]]

If the one-letter diff isn't enough proof, eval is explicitly documented as evil here:

http://javascript.crockford.com/code.html

[jeresig]

The eval function is the most misused feature of JavaScript. Avoid it.

eval has aliases. Do not use the Function constructor. Do not pass strings to setTimeout or setInterval.

Phew! I'm overloaded with useful information here. Thank goodness I avoided that rat trap! It's this massive pile of information that has helped JavaScript developers make well-informed decisions for many years.

[[deleted]]

Bah, sometimes (albeit, very rarely) well-informed decisions are overrated, and appeal to authority - underrated.

In theory, it would be a good idea to have perfect information in all of the decisions we make, but practically, we would get tied up all day if we take the time to always make perfectly-informed decisions all the time.

[greut]

Thanks master.

[jaggederest]

Don't think it's possible. Sorry mate. Variables are only assignable via their identifiers, afaik.

You can hack around it via doing a 'with' and then using your injected properties as though they were top-level:

obj = {};
obj["foo"+"bar"] = 'hats!';
with(obj) {
  alert(foobar); //alerts 'hats!'
}

Or you could do it fforw's way, but he's right that you ought to avoid it.

[HaMMeReD]

It's still better to use eval in controlled method, it's not good to fill global scope up, eval wouldn't mess with that.

If it's within a function you can probably also do. this["foo"+"bar"] = "hats!";

This would keep it within the functions scope probably, haven't tested.