2018-06-04 ES5的mixin模式，ES6的Objec

1. mixin

function mixin(a,b){
  for(let key in b){
    a[key] = b[key]
  }
}

将b的每一项拷贝到a上，深拷贝

2. Object.assign
   相当于

Object.assign(a,b)