<!DOCTYPE html>
<html >
<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>
<script src="vue.js"></script>
</head>
<body>
<div >
<input type="text" v-model="firstName">+
<input type="text" v-model="lastName">=
<input type="text" v-model="fullName">
</div>
</body>
<script>
//创建一个vue实例
//当我们导入包之后，在浏览器的内存中就多了一个vue构造函数
var vm = new Vue({
el: '#app',//表示当前我们new的这个vue实例要控制页面上的哪个区域
data: { //data属性中存放的是el中要用到的数据
firstName: '',
lastName: '',
fullName: '',
},
watch:{
//watch可以监听data中指定数据的变化，然后触发对应的处理函数
firstName:function(newVal,oldVal){
//console.log('firstName变化')
//this.fullName = this.firstName+'_'+this.lastName
this.fullName = newVal+'_'+this.lastName
},
lastName:function(newVal,oldVal){
this.fullName = this.firstName+'_'+newVal
}
}
});
</script>
</html>