子組件經過 $emit 觸發父組件的自定義事件

子組件：

<template>
  <div class="train-city">
    <h3>父組件傳給子組件的toCity:{{sendData}}</h3> 
    <br/><button @click='select(`大連`)'>點擊此處將‘大連’發射給父組件</button>
  </div>
</template>
<script>
  export default {
    name:'trainCity',
    props:['sendData'], // 用來接收父組件傳給子組件的數據
    methods:{
      select(val) {
        let data = {
          cityname: val
        };
        this.$emit('showCityName',data);//select事件觸發後，自動觸發showCityName事件
      }
    }
  }
</script>

　　父組件：

<template>
    <div>
        <div>父組件的toCity{{toCity}}</div>
        <train-city @showCityName="updateCity" :sendData="toCity"></train-city>
    </div>
<template>
<script>
  import TrainCity from "./train-city";
  export default {
    name:'index',
    components: {TrainCity},
    data () {
      return {
        toCity:"北京"
      }
    },
    methods:{
      updateCity(data){//觸發子組件城市選擇-選擇城市的事件
        this.toCity = data.cityname;//改變了父組件的值
        console.log('toCity:'+this.toCity)
      }
    }
  }
</script>