1. require()
load module
http://stackoverflow.com/questions/9901082/what-is-this-javascript-require
https://nodejs.org/api/modules.html#modules_module_require_id
http://openmymind.net/2012/2/3/Node-Require-and-Exports/
原文：http://www.cnblogs.com/phoenix13suns/p/5328596.html