vue3已废除sync写法，v-model代替
实现state的值可以从子组件传递给父组件，也可以从父组件传递给子组件

文件地址pages/about/about.vue
<template>
	<view>
		<button size="mini" @click="clickBtn">开启{{mystate}}</button>
		<mypop v-model:state="mystate"></mypop>
	</view>
</template>

<script>
	export default {
		data() {
			return {
				mystate:false
			};
		},
		methods:{
			clickBtn(){
				this.mystate=true
			},
		}
	}
</script>

<style lang="scss">

</style>

文件地址components/mypop/mypop.vue
<template>
	<view>
		<view>---弹出框样式---</view>
		<view class="box" :style="{height:state?'300rpx':'0'}">
			{{state}}
		</view>
		<button size="mini" @click="closeBtn"> 关闭{{state}}</button>
	</view>
</template>

<script>
	export default {
		name:"mypop",
		data() {
			return {
				
			};
		},
		props:{
			state:{
				type:Boolean,
				default:false
			}
		},
		methods:{
			closeBtn(){
				this.$emit("update:state",false)
			}
		}
	}
</script>

<style lang="scss">
.box{
	width: 300rpx;
	height: 300rpx;
	background: pink;
}
</style>