1.后动实现v-model的双向数据绑定

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <div>
    <div class="app">
      <input type="text" v-model="inputValue">
      {{inputValue}}
    </div>
  </div>
  <script>

    function observe(data) {
      if (!data && typeof data !== 'object'){
        return;
      }
      Object.keys(data).forEach(key => {
        defineReactive(data, key, data[key]);
      })
    }

    function defineReactive(data, key, value) {
      observe(value);
      var dep = new Dep();
      Object.defineProperty(data, key, {
        get: function(){
          console.log(222)
          if(Dep.target){
            dep.addSub(Dep.target)
          }
          return value;
        },
        set: function(newVal){
          if(value == newVal){
            return;
          }
          value = newVal;
          dep.notify();
        }
      })
    }
    
   function Dep(){
     this.subs = [];
   }
   Dep.prototype = {
     addSub(sub){
      this.subs.push(sub);
     },
     notify(){
      this.subs.forEach(sub =>{
        console.log(sub)
          sub.update();
      })
     }
   }


   //订阅器实现
   function Watcher(node, vm ,name){
     Dep.target = this;
      this.vm = vm;
      this.node = node;
       = name;
      this.update();
      Dep.target = null;
   }

   Watcher.prototype = {
    update(){
      this.get();
      if(this.node.nodeType === 3){
        this.node.nodeValue = this.value;
      }else{
        this.node.value = this.value;
      }
    },
    get(){
      this.value = this.vm.$data[];//添加订阅器
    }
   }



 var vm1 =  new Vue({
    el: ".app",
    data: {
      inputValue: 40
    }
  })

  function Vue(options){
    this.$data = options.data;
    observe(options.data);
    var originDom = document.querySelector(options.el);
    //需要进行编译，解析指令
    var fragment = nodeToFragment(originDom, this);
    document.querySelector(options.el).appendChild(fragment);
  }

  function nodeToFragment(node, vm){
    var frameEle = document.createDocumentFragment();
    var child;
    while(child = node.childNodes[0]){
      compile(child, vm);
      frameEle.append(child);
    }
    return frameEle;
  }


  function compile(node, vm){
    if (node.nodeType === 1) { //元素节点
        for(var i=0; i < node.attributes.length; i++) {
          if(node.attributes[i].nodeName === 'v-model'){
            var name = node.attributes[i].nodeValue;
            node.value = vm.$data[name];
            node.addEventListener('input', function(e){
              vm.$data[name] = e.target.value;
            })
            node.removeAttribute('v-model');
          }
        }
      new Watcher(node, vm, name);  
    }
    if(node.nodeType === 3){
      let reg = /\{\{(.*)\}\}/;    // {{xxx}}
      if(reg.test(node.nodeValue)){
        //console.log(node.nodeValue,RegExp.$1)
        var name = RegExp.$1;
        node.nodeValue = vm.$data[name];
      }
      new Watcher(node, vm, name);
    } 
  }

  setTimeout(()=>{
    vm1.$data.inputValue = 80;
  },2000)
  </script>
</body>
</html>