箭头函数里的this

var a = {
       name: 'li',
       say: (word) => {
           console.log(this)
           console.log(word)
       }
   }
  a.say('hi')
这个是window

var a = {
       name: 'li',
       say: function(word){
           console.log(this)
           console.log(word)
       }
   }
  a.say('hi')
这个是a对象本身

http://blog.csdn.net/liwusen/article/details/70257837 一点没说清
http://blog.csdn.net/u013344815/article/details/73184928 最后的两句总结和废话差不多