function observe(value, cb) {
 Object.keys(value).forEach((key) => defineReactive(value, key, value[key] , cb))
}

function defineReactive (obj, key, val, cb) {
 Object.defineProperty(obj, key, {
  enumerable: true,
  configurable: true,
  get: ()=>{
   /*....依賴收集等....*/
   /*Github:https://github.com/answershuto*/
   return val
  },
  set:newVal=> {
   val = newVal;
   cb();/*訂閱者收到消息的回調(diào)*/
  }
 })
}

class Vue {
 constructor(options) {
  this._data = options.data;
  observe(this._data, options.render)
 }
}

let app = new Vue({
 el: '#app',
 data: {
  text: 'text',
  text2: 'text2'
 },
 render(){
  console.log("render");
 }
})

_proxy.call(this, options.data);/*構(gòu)造函數(shù)中*/

/*代理*/
function _proxy (data) {
 const that = this;
 Object.keys(data).forEach(key => {
  Object.defineProperty(that, key, {
   configurable: true,
   enumerable: true,
   get: function proxyGetter () {
    return that._data[key];
   },
   set: function proxySetter (val) {
    that._data[key] = val;
   }
  })
 });
}

new Vue({
 template: 
  `<div>
   <span>text1:</span> {{text1}}
   <span>text2:</span> {{text2}}
  <div>`,
 data: {
  text1: 'text1',
  text2: 'text2',
  text3: 'text3'
 }
});

class Dep {
 constructor () {
  this.subs = [];
 }

 addSub (sub: Watcher) {
  this.subs.push(sub)
 }

 removeSub (sub: Watcher) {
  remove(this.subs, sub)
 }
 /*Github:https://github.com/answershuto*/
 notify () {
  // stabilize the subscriber list first
  const subs = this.subs.slice()
  for (let i = 0, l = subs.length; i < l; i++) {
   subs[i].update()
  }
 }
}
function remove (arr, item) {
 if (arr.length) {
  const index = arr.indexOf(item)
  if (index > -1) {
   return arr.splice(index, 1)
 }
}

class Watcher {
 constructor (vm, expOrFn, cb, options) {
  this.cb = cb;
  this.vm = vm;

  /*在這里將觀察者本身賦值給全局的target，只有被target標(biāo)記過(guò)的才會(huì)進(jìn)行依賴收集*/
  Dep.target = this;
  /*Github:https://github.com/answershuto*/
  /*觸發(fā)渲染操作進(jìn)行依賴收集*/
  this.cb.call(this.vm);
 }

 update () {
  this.cb.call(this.vm);
 }
}

class Vue {
 constructor(options) {
  this._data = options.data;
  observer(this._data, options.render);
  let watcher = new Watcher(this, );
 }
}

function defineReactive (obj, key, val, cb) {
 /*在閉包內(nèi)存儲(chǔ)一個(gè)Dep對(duì)象*/
 const dep = new Dep();

 Object.defineProperty(obj, key, {
  enumerable: true,
  configurable: true,
  get: ()=>{
   if (Dep.target) {
    /*Watcher對(duì)象存在全局的Dep.target中*/
    dep.addSub(Dep.target);
   }
  },
  set:newVal=> {
   /*只有之前addSub中的函數(shù)才會(huì)觸發(fā)*/
   dep.notify();
  }
 })
}

Dep.target = null; //防止依賴重復(fù)添加

<template>
 <div>
 {{a+b}}
 </div>
 <div>
 {{a-c}}
 </div>
</template>

<script>
let app = new Vue( {
 data :{
  a: 1,
  b: 2,
  c: 3
 }
 })