vue 生命周期理解

时间 2019-11-29

标签 vue 生命周期理解繁體版

原文原文链接

先上一张生命周期的图：javascript

8个生命周期：html

beforeCreate:组件实例刚被建立，组件属性计算以前

created:组件实例建立完成，属性已绑定，但DOM还未生成，$el属性还不存在

beforeMount:模板编译/挂载以前

mounted:模板编译/挂载以后

beforeUpdate:组件更新以前

updated:组件更新以后

brforeDestroy:组件销毁前调用

destroyed:组件销毁后调用

生命周期探究

对于执行顺序和何时执行，看上面两个图基本有个了解了。下面咱们将结合代码去看看钩子函数的执行。vue

先上一段代码：java

<!DOCTYPE html>
<html>
<head>
    <title></title>
    <script type="text/javascript" src="https://cdn.jsdelivr.net/vue/2.1.3/vue.js"></script>
</head>
<body>

<div id="app">
     <p>{{ message }}</p>
</div>

<script type="text/javascript">
    
  var app = new Vue({
      el: '#app',
      data: {
          message : "xuxiao is boy" 
      },
       beforeCreate: function () {
                console.group('beforeCreate 建立前状态===============》');
               console.log("%c%s", "color:red" , "el     : " + this.$el); //undefined
               console.log("%c%s", "color:red","data   : " + this.$data); //undefined 
               console.log("%c%s", "color:red","message: " + this.message)  
        },
        created: function () {
            console.group('created 建立完毕状态===============》');
            console.log("%c%s", "color:red","el     : " + this.$el); //undefined
               console.log("%c%s", "color:red","data   : " + this.$data); //已被初始化 
               console.log("%c%s", "color:red","message: " + this.message); //已被初始化
        },
        beforeMount: function () {
            console.group('beforeMount 挂载前状态===============》');
            console.log("%c%s", "color:red","el     : " + (this.$el)); //已被初始化
            console.log(this.$el);
               console.log("%c%s", "color:red","data   : " + this.$data); //已被初始化  
               console.log("%c%s", "color:red","message: " + this.message); //已被初始化  
        },
        mounted: function () {
            console.group('mounted 挂载结束状态===============》');
            console.log("%c%s", "color:red","el     : " + this.$el); //已被初始化
            console.log(this.$el);    
               console.log("%c%s", "color:red","data   : " + this.$data); //已被初始化
               console.log("%c%s", "color:red","message: " + this.message); //已被初始化 
        },
        beforeUpdate: function () {
            console.group('beforeUpdate 更新前状态===============》');
            console.log("%c%s", "color:red","el     : " + this.$el);
            console.log(this.$el);   
               console.log("%c%s", "color:red","data   : " + this.$data); 
               console.log("%c%s", "color:red","message: " + this.message); 
        },
        updated: function () {
            console.group('updated 更新完成状态===============》');
            console.log("%c%s", "color:red","el     : " + this.$el);
            console.log(this.$el); 
               console.log("%c%s", "color:red","data   : " + this.$data); 
               console.log("%c%s", "color:red","message: " + this.message); 
        },
        beforeDestroy: function () {
            console.group('beforeDestroy 销毁前状态===============》');
            console.log("%c%s", "color:red","el     : " + this.$el);
            console.log(this.$el);    
               console.log("%c%s", "color:red","data   : " + this.$data); 
               console.log("%c%s", "color:red","message: " + this.message); 
        },
        destroyed: function () {
            console.group('destroyed 销毁完成状态===============》');
            console.log("%c%s", "color:red","el     : " + this.$el);
            console.log(this.$el);  
               console.log("%c%s", "color:red","data   : " + this.$data); 
               console.log("%c%s", "color:red","message: " + this.message)
        }
    })
</script>
</body>
</html>

打印的结果以下：chrome

得出：segmentfault

beforeCreate:el和data并未初始化，app

created:完成data数据的初始化,el没有dom

beforeMount：完成el和data的初始化，上图红框处，发现el仍是{{message}}，这就是虚拟DOM技术，先把坑占住了，到后面mounted的时候再把值渲染进去函数

mounted:完成挂载this

update 相关

这里咱们在 chrome console里执行如下命令：

app.message= 'yes !! I do';

下面就能看到data里的值被修改后，将会触发update的操做。

destroy 相关

咱们在console里执行下命令对 vue实例进行销毁。销毁完成后，咱们再从新改变message的值，vue再也不对此动做进行响应了。可是原先生成的dom元素还存在，能够这么理解，执行了destroy操做，后续就再也不受vue控制了。

app.$destroy();

生命周期总结

这么多钩子函数，咱们怎么用呢，我想你们可能有这样的疑问吧，我也有，哈哈哈。

参考：http://www.cnblogs.com/gagag/p/6246493.html

https://segmentfault.com/q/1010000007704114?_ea=1431323

https://segmentfault.com/a/1190000008010666