Let me just clarify -- creating large closures to wrap libraries in -- that kind of thing is good. The (function(){...})(); pattern is excellent for not polluting the global variable namespace. And single library objects are great too -- they're generally only created once, so there's no memory leaks.

And closures for things like callbacks for AJAX etc. -- these are generally fine, because once the AJAX returns and the callback function finishes executing, then once the AJAX object gets garbage-collected, the callback will too, and its closure.

But if you're leaving "infinite-lived" references around to functions within closures, repeatedly, whether it's via an infinitely long setInterval, or whether you're just storing function references in some array you build up and never remove from -- that's just bad programming. Of course it's a "memory leak", but you, the programmer, intentionally asked for it. It's not the language's fault -- that's how the language is supposed to work.