Proxy

这个说的Proxy 是es6中新增功能，可以用来自定义对象中的操作

let p = new Proxy(target, handler)
// target 代表需要添加代理的对象
// handler 用来自定义对象中的操作

可以很方便地使用Proxy来实现一个数据绑定和监听

let onWatch = (obj, setBind, getLogger) => {
  let handler = {
    get(target, property, receiver) {
      getLogger(target, property)
      return Reflect.get(target, property, receiver)
    },
    set(target, property, value, receiver) {
      setBind(value)
      return Reflect.set(target, property, value)
    }
  }
  return new Proxy(obj, handler)
}

let obj = {a: 1}
let value
let p = onWatch(obj, v => {
  value = v
}, (target, property) => {
  console.log(`Get '${property}' = ${target[property]}`)
})
p.a = 2 // bind 'value' to '2'
p.a // -> Get 'a' = 2