给input元素绑定原生input事件，触发input事件时，进而触发update:model-value事件

<template>
<Child v-model="lastName" v-if="true"></Child>
<p >{{lastName}}</p>
</template>
<script>
import Child from "./components/child.vue"
data() {return {lastName: '我是父组件'};},
</script>

子组件

<template><div>我是child组件<!-- <input type="text" :value="lastName" @input="$emit('update', $event.target.value)"> --><input type="text" v-model="input"></div>
</template>
<script>
export default {name: 'Child',props: ['lastName'],model:{prop: 'lastName',event: 'update'},data() {return {// value: this.lastName,}},computed: {input: {get() {return this.lastName;},set(val) {this.$emit('update', val);    // 触发}}},mounted() {},methods: {},}
</script>