Helping Javascript code completion

The code completion in IntelliJ is really quite great, but javascript is so dynamic, it's impossible to get it up to snuff with other languages.

What I want to know is there a way to help the completion engine to make it more accurate (not completing on a global scope).  Can I somehow tell the editor what type a variable is?

For instance, in python I would do:
assert isinstance(obj, type)

Is there a way to give IntelliJ's editor / code completion engine hints?  Is it code comments (with types)?

Jason