<template>
<div class="demo-Directives-If">
<span>{{msg}}</span>
<button>刷新</button>
</div>
</template>
<script>
import Vue from 'vue'
export default {
name: "demo-Directives-If",
};
window.onload = function () {
new Vue({
el: '.demo-Directives-If',
data: {
msg: 'Hello Vue!'
}
})
}
</script>
初次用vue cli 3 这里报错msg未定义,请问msg该如何声明呢