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我们学习一门新语言或者框架时,第一件事是什么呢,那必然是向世界say Hello。

创建一个Vue应用

话不多说,先上代码,让我们感受一下Vue的核心功能

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <div id="app">
        <input type="text" v-model="message">
        <h1>{{message}}</h1> // {{message}}模板的输出方式
    </div>
    <script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
    <script type="text/javascript">
        var app = new Vue({
            el: '#app', // app是Vue实例的挂在对象
            data: {
                message: "Hello world" // 字面量
            }
        })
    </script>
</body>
</html>

当修改输入框内容时,h1标签内容也做相应改变,虽然代码很简单,还是能体会到双向绑定的精髓。

双向绑定(面试考点)

  1. 通过构造函数创建一个Vue实例 new Vue(),此时app就相当于 new Vue;
  2. 传入el,el是Vue对象中必不可少的,需要把el挂载到页面已存在的DOM(可以是DOM元素,或者是CSS选择器)上;

     var app = new Vue({
         el: '#app', // 或者document.getElementById('app')
     })
  3. 在input标签上有一个v-model指令,它的值和Vue实例中data里的message对应,input可以修改message的值,同时当message改变时也可以体现在视图上;

生命周期(开发时必了解)

每个Vue实例在被创建之前都要经过一系列的初始化过程,这个过程就Vue的生命周期。下面是Vue的几个钩子函数:

beforeCreate: function () {
    console.group('beforeCreate 创建前状态===============》');
    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 创建完毕状态===============》');
    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)
}

下图是Vue生命周期过程中el、data以及data里面的message字段的变化
1.png

2.png

以上是本期全部内容,欲知后事如何,请听下回分解<( ̄︶ ̄)↗[GO!]


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