// 子组件中
<template>
	<div class="com_a">
		<span>{{messageA}}</span>
		<p>获取父组件的值为: {{parentVal}}</p>
	</div>
</template>

<script>
	export default {
		data() {
			return {
				messageA: 'this is old'
			}
		},
		computed: {
			parentVal() {
				return this.$parent.msg;
			}
		}
	}
</script>