原贴地址：http://pierrespring.com/2010/05/11/function-scope-and-lexical-scoping/
个人觉得写得不错，简单地搬运，如有错误，请指正。
Wikipedia defines Scope as follows:
Tipically, scope is used to define the extent of information hiding--that is, the visibility or accessibility of
variables from diefferent parts of the program.
作用域是用来定义信息隐藏的深度--程序中，其它地方对某个部分中的变量的可访问性。
In JavaScript we have Function Scope and Lexical Scope.
Function Scope means that any variable which is defined within a function is visible within that entire function.
This is quite different form Block Scope, in which a variable scope is limited by the block a variable is declared in.
Function Scope 是指，任何在函数内部定义的变量是对整个函数都可见的。
JavaScript的Function Scope and Lexical Scope
原文：http://www.cnblogs.com/Yaxian/p/4510030.html