# 实例生命周期钩子

简单理解，生命周期钩子函数就是vue实例在某一个时间点会自动执行的函数。

<div id="app">{{msg}}</div>

<script src="https://cdn.bootcss.com/vue/2.4.2/vue.js"></script>
<script>
  var vm = new Vue({
    el: '#app',
    data: {
      msg: 'Vue的生命周期'
    },
    beforeCreate: function() {
      console.group('------beforeCreate创建前状态------');
      console.log("el     : " + this.$el); //undefined
      console.log("data   : " + this.$data); //undefined 
      console.log("msg: " + this.msg) //undefined 
    },
    created: function() {
      console.group('------created创建完毕状态------');
      console.log("el     : " + this.$el); //undefined
      console.log("data   : " + this.$data); //已被初始化 
      console.log("msg: " + this.msg); //已被初始化
    },
    beforeMount: function() {
      console.group('------beforeMount挂载前状态------');
      console.log(this.$el);// <div id="app">{{msg}}</div> 挂载前状态
    },
    mounted: function() {
      console.group('------mounted 挂载结束状态------');
      console.log(this.$el);// <div id="app">Vue的生命周期</div>   msg内容被挂载并渲染到页面
    },
      // 当data被修改之前
    beforeUpdate: function () {
      console.group('beforeUpdate 更新前状态===============》');
      console.log("el     : " + this.$el);
      console.log(this.$el);   
      console.log("data   : " + this.$data); 
      console.log("msg: " + this.msg); 
    },
      // 触发beforeUpdate之后，虚拟DOM重新渲染并应用更新
      // 当data被修改之后
    updated: function () {
      console.group('updated 更新完成状态===============》');
      console.log("el     : " + this.$el);
      console.log(this.$el); 
      console.log("data   : " + this.$data); 
      console.log("msg: " + this.msg); 
    },
      // 调用vm.$destroy() 销毁前
    beforeDestroy: function () {
      console.group('beforeDestroy 销毁前状态===============》');
      console.log("el     : " + this.$el);
      console.log(this.$el);    
      console.log("data   : " + this.$data); 
      console.log("msg: " + this.msg); 
    },
       // 调用vm.$destroy() 销毁后
    destroyed: function () {
      console.group('destroyed 销毁完成状态===============》');
      console.log("el     : " + this.$el);
      console.log(this.$el);  
      console.log("data   : " + this.$data); 
      console.log("msg: " + this.msg)
    }
  })
</script>

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# Demo

See the Pen 生命周期钩子 by xugaoyi (@xugaoyi) on CodePen.

# 生命周期图示

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