ComponentA.vue

<template>
<div>
  <span>ComponentA: {{ title }}</span>
  <button @click="back">回調</button>
</div>
</template>

<script>

export default {
name: 'ComponentA',
props: {
  title: String
},
methods: {
  back () {
    console.log('back')
    this.title = '回調了'
    this.$emit('titleChanged', '子向父組件傳值')
  }
}
}
</script>

<style scoped>

</style>

HelloWorld.vue

<template>
    <component-a :title='title' @titleChanged="onTitleChanged"></component-a>
  </div>

</template>

<script>
import ComponentA from '@/components/ComponentA'

export default {
  name: 'test',
  components: {
    ComponentA
  },
  data () {
    return {
      title: '向ComponentA傳值',
    }
  },
  methods: {
    onTitleChanged (e) {
      console.log('ontitleChanged', e)
    },
}
</script>

<style scoped>

</style>

點擊ComponentA 中的按鈕：回調，title值修改成功了，但是會拋出vue的一個警告：

[Vue warn]: Avoid mutating a prop directly since the value will be overwritten whenever the parent component re-renders. Instead, use a data or computed property based on the prop's value. Prop being mutated: "title"

found in

---> <ComponentA> at src/components/ComponentA.vue
       <Test> at src/components/HelloWorld.vue
         <App> at src/App.vue
           <Root>

經過研究發現一種修改方式：sync修飾符

修改ComponentA中的back方法：

 back () {
      console.log('back')
      // this.title = '回調了'
      this.$emit('titleChanged', '子向父組件傳值')
      this.$emit('update:title', 'newTitle')
    }

修改HelloWorld中的布局：

    <component-a :title.sync='title' @titleChanged="onTitleChanged"></component-a>