须知：vue里子组件无法改变父组件的值

思路：

1. 父组件定义数据 —— const data = ref(false)

2. 把值传递给子组件 —— :sendData = "data"

3. 子组件接收数据，使用、修改完成后 —— props: ["sendData"] —— const a = props.sendData —— a = true

4. 触发父组件事件，传值 —— emit("emitEffect", { emit: a })

5. 被触发的父组件，接收值，并更新自己最开始定义的数据 —— @emitEffect = "changeData" —— const changeData = (value) => { data = value.a }

例子：

父组件：

<template>
    <div class="index">
        <div class="index__nav">
            <Indexnav :changeNavFu=changeNavFu @changeNavfu="changeNav" />
        </div>
    </div>
</template>

<script>
import { ref } from 'vue'
import Indexnav from './Indexnav.vue'

export default {
    name: 'index',
    components: { Indexnav, Indextab },

    setup () {

        const changeNavFu = ref(false)

        const changeNav = (val) => {
            changeNavFu.value = val.data
            console.log(val)                 // {data:false}
        }

        return { changeNavFu, changeNav }
    }
}
</script>

<style lang="scss" scoped>
.index{
    font-size: .13rem;
    overflow: hidden;
    width: 100%;
    height: 100vh;
    &__nav {
        width: 2rem;
    }
}
</style>

子组件：

<template>
    <div class="Indexnav" :style="isCollapse?'width:.63rem':''">

        <div class="Indexnav__header" @click="changeNav">
            <div :class="isCollapse?'sider-toggler':'sider-toggler active'"></div>
        </div>

    </div>
</template>

<script>
import { ref } from 'vue'

export default {
    name: 'Indexnav',
    components: { Location },

    props: ['changeNavFu'],

    setup (props, { emit }) {           // 一定要记得把props和emit传入setup函数
        
        const isCollapse = ref(props.changeNavFu)

        const changeNav = () => {
            isCollapse.value = !isCollapse.value
            emit('changeNavfu', { data: isCollapse.value })
        }
        return { isCollapse, changeNav }
    }
}
</script>

<style lang="scss" scoped>
@import '../../assets/fonts/iconfont.css';

.Indexnav{
    position: absolute;
    width: 2rem;
    top: 0;
    left: 0;
    height: 100%;
    box-shadow: .01rem .02rem .1rem rgba(0,0,0,.5);
    border-right: 1px solid #f2f4f9;
    transition: all .1s linear;
}
</style>