<div id="app">
{{msg}}
</div>
<script>
var app = new Vue({
el: "-sharpapp",
data: {
msg: "Hello Vue"
}
})
app.msg=123
console.log(app.msg)
console.log(app.$data.msg === app.msg)
</script>when the above code is created by var, the two print messages execute normally, and when created by new Vue, the second print message reports an error. What is the difference between the two methods?