v-model 只能运用到表单元素中
如input（redio,text,address,emll......） select checkbox textarta
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<body>
<div id="app">
<h4>{{msg}}</h4>
<input type="text" v-model:value="msg" style=" 100%;">
</div>
</body>
<script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
<script>
var app= new Vue({
el:'#app',
data:{
msg:'大家好'
},
methods:{}
})
</script>
</html>