<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>计算属性与侦听器</title>
<script src="./vue.js"></script>
</head>
<body>
<div id="root">
姓：<input v-model="firstName"/>
名：<input v-model="lastName"/>
<div>{{fullName}}</div>
</div>
<script>
new Vue({
el:"#root"
data:{
firstName:'',
lastName:''
},
computed:{
fullName:function(){
return this.firstName+' '+this.lastName
}
}
})
</script>
</body>
</html>
之间需要用逗号隔开，你的#root后没有逗号