Will this kind of codes leak memory?
No, there is nothing you're doing in that code that would result in memory leaks.

I found an article written by Jack Slocum (creator of the ExtJS framework) that details some basic steps to follow to avoid memory leaks. The original article is a bit dated and browsers have gotten a lot better at cleaning up memory, so I don't know how much of it still applies to the latest browsers (it certainly applies to older versions of IE and Firefox).

Here is the article: http://maxthonuser.blogspot.com/2008/02/easy-steps-to-avoid-javascript-memory.html

Relevant text (in case the link ever dies):


  It's as simple as these 3 steps:
  
  
  Never put anything in a DOM expando or property other than a primitive value unless you plan on cleaning it up.
  This is the most important rule of all. It may seem convenient to put your JS object in a DOM expando, so you can $() and get it, but don't do it. Sure, I know what you are thinking, I am being a little paranoid. There are lots of instances where putting a JS Object in a DOM expando won't cause a leak. That's true, but there are also many that will... some which are not so easy to detect (i.e. closures). So to avoid the possibility all together, I follow this simple rule.
  Clean up all your DOM event handlers on unload if there's a chance they could reference a DOM object.
  There's no reason to manually do this when there are libraries that do it automatically. I use YAHOO.util.Event for all my event handlers, it handles this for me automagically. Other libraries (prototype, dojo, etc) have some sort of mechanism to do the same thing, although I'm not sure how effective they are. If you look at the leak images above once again, you will notice almost all of them are in event related code of those libraries.
  Set your XMLHttpRequest onreadystatechange handlers to null when you are done with them.
  I use YAHOO.util.Connect for all my XHR connections and it uses a polling mechanism instead of readstate, so I don't need to do this anymore. If you can switch to YAHOO.util.Connect (or YAHOO.ext.UpdateManager built on top of it), I'd recommend it.