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不废话，直接上源码

function vue() {  this.$data = { aaa: 1 };  this.el = document.getElementById('app');  this.virtualdom = '';  this.observe(this.$data);  this.render()}vue.prototype.observe = function (obj) {  var self = this;  var value;  for (var key in obj) {    value = obj[key];    if (typeof value == 'object') {      this.observe(value)    } else {      Object.defineProperty(this.$data, key, {        get: function () {          // 收集依赖          return value        },        set: function (newValue) {          // 调用notify(), 进行diff运算，调用render()，          value = newValue;          self.render()        }      })    }  }}vue.prototype.render = function () {  this.virtualdom = 'i am ' + this.$data.aaa;  this.el.innerHTML = this.virtualdom;}

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