TODO READING

http://www.html-js.com/article/JavaScript-tips-on-how-to-implement-a-ECMAScript-6-promise-patch 如何实现一个ECMAScript 6 的promise功能

http://bg.biedalian.com/2014/03/01/I-promise-I-resolve-v2.html

http://www.html-js.com/article/1752

http://mao.li/javascript/javascript-callback-function/