References between vue components

I want to reference a dom,
on a component, but print it out as undefined,. How to reference this

<template>
    <div ref="a"></div>
    <show :dom="$refs.a"/>
</template>

show.vue

    export default {
    name: "show",
    props: {
        dom: String,
        params: Object,
    },
    mounted() {
        console.log(".........",this.dom); //undefinde
    },
};
Mar.20,2021

Sorry! I'm confused about the concept of ref.
to copy an official document:

important note about ref registration time: because ref itself is created as a rendering result, you can't access them during initial rendering-they don't exist yet! $refs is not responsive either, so you should not try to use it for data binding in templates.

if you want to access the dom structure of the parent component in the child component, you can pass it in by binding data.

MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1ead163-2129.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1ead163-2129.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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