输入框下面显示{firstName}{lastName}是怎么回事？
<!DOCTYPE html>
<html lang ="en">
<head>
<meta charest="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>{{firstName}}{{lastName}}</div>
</div>
<script>
new vue({
el:"#root"
data:{
firstName:'',
lastName:''
}
})
</script>
</body>
</html>
