多组件生命周期关系：
    父beforeCreate->父created->父beforeMount（子周期）父mounted
    子周期： 子beforeCreate->子created->子beforeMount->子mounted
    子的created可以拿父的数据了
实例属性:

    $children 父抓子元素

    $parent 子抓父元素

父A
<template>
    <div>
        <h3>CompA数据</h3>
        <hr>
        <CompB></CompB>
    </div>
</template>
<script>
import CompB from './CompB'
export default {
    name:'CompA',
        data() {
        return {
        msg:'a数据'
        }
    },
    methods: {
        show(){
        console.log("a方法")
        }
    },
    components:{CompB}，
mounted() {
    console.log("a抓取b数据",this.$children)
  },
}
</script>

子B
<template>
    <div>
        <h3>CompB数据</h3>
        <hr>
        <CompC></CompC>
    </div>
</template>
<script>
import CompC from './CompC'
export default {
    data() {
        return {
            msg:'b数据'
    }
    },
    methods: {
        show(){
        console.log("b方法")
        }
    },
    components:{CompC},
    created() {
        console.log('b抓取a数据',this.$parent)
    },
}
</script>