The browsers are getting better at optimizing memory use for small closures all the time, but there's still a long way to go. Here's a screenshot of the Chrome heap profiler for both cases:

http://cl.ly/A5NX

I have one question. How to handle private methods in prototype/module pattern? If I declare private function in obj function declaration I can not access it in public functions attached to the prototype of obj. This is also true for module pattern. This problem arises when I need to add extra method later. How to overcome this situation?

You can use a heap snapshot in Chrome Dev Tools. It has a handy feature where you take multiple snapshots and it shows you the differences in memory usage between them. See: http://code.google.com/chrome/devtools/docs/heap-profiling.h...

I'll definitely be looking into that. Thanks.