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/