箭头函数

• https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Functions/Arrow_functions
• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions
• https://hacks.mozilla.org/2015/06/es6-in-depth-arrow-functions/
• http://www.infoq.com/cn/articles/es6-in-depth-arrow-functions

简单总结就是一句话： 能用箭头函数的地方就别用function定义！