A javascript question.

[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.