function

first class

1. first class citizen:
   1. passed as an argument;
   2. be returned as result of funtions;;
   3. assigned to a variable

anonymous function;

1. have no name;

scope

1. what? 一块区域,在这个区域声明的变量只在这个区域(以及下级区域)可见

2. types:

   1. block scope: in block;
   2. function scope: in funciton
   3. gloabl scope: global

3. lexical scope/ static scope vs dymanic scop

   1. 编译时决定了变量可见范围
   2. 运行时再决定变量可见范围