1. this
var name=222
var a={
name:111,
say:function(){
console.log(this.name)
}
}
var fun=a.say
fun() //fun.call(window) //222
a.say() //a.say.call(a) //111
var b={
name:333,
say:function(fn){
fn()
}
}
b.say(a.say) //fn() fun.call(window) //222
b.say=a.say //把a里的say函数直接赋值给b.say
b.say() //b.say.call(b) //333通过使用call来确定this指向。
2. 箭头函数的this指向
