If you want to master Javascript, what do you need to know:

  * javascript Object
  * this & with
  * JavaScript Constructor
  * Prototype
  * Closure
  * Inheritance
  * Namespace



Closure

A "closure" is an expression (typically a function) that can have free variables together with an environment that binds those variables (that "closes" the expression). 



F.Y.I

http://jibbering.com/faq/notes/closures/ (english version)

http://www.cn-cuckoo.com/2007/08/01/understand-javascript-closures-72.html  (english version)

http://www.crockford.com/javascript/