Question

var Obj = function(){}; var X = new Obj();

will X = null properly clear memory?

Also would this be equivalent?

var Obj = function(){}; 
var X   = {}; 
X.obj   = new Obj();
delete(X.obj);

EDIT
It would seem that although deleting X.obj would NOT immediately clear memory, it would help the garbage collection. If I don’t delete X.obj, there would still be a pointer to an object and so the GC may not clean it up.

Although I’m picking @delnan’s answer, if you’re reading this you should def also catch Benubird’s article.

I also notice I accidentally wrote delete(X) originally instead of delete(X.obj) – sorry.

Answer 1

The short answer is that you don’t. delete simply removes a reference (and not in the way you try to use it, see the above link – delete is one of those language features few people actually understand), nothing more. The implementation clears memory for you, but it’s not your business when (and even if, strictly speaking – this is why one shouldn’t rely on finalizers in GC’d languages that offer them) it does. Note though:

• Only objects that can be proven to be unreachable (i.e. no way to access it) to all code can be removed. What keeps references to whom is usually fairly obvious, as least conceptually. You just need to watch out when dealing with lots of closures, as they may capture more variables than you think. Also note that circular references are cleaned up properly.
• There’s a bug in old (but sadly still used) IE versions involving garbage collection of JS event handlers and DOM elements. Google (perhaps even SO) should have better material on my memory.

On the plus side, that means you won’t get dangling pointer bugs or (save of course the aforementioned pitfalls) memory leaks.