What is the usage of emit in vue

In vue, emit is used by sub-components to call methods of parent components and pass data; sub-components can use "$emit" to trigger custom events of parent components. After the event is triggered, additional parameters will be passed to the listener. Callback, the syntax is "vm.$emit(event, arg)".

The operating environment of this article: Windows 10 system, Vue version 2.9.6, DELL G3 computer.

What is the usage of emit in vue

For the definition of $emit in vue, see:

vm.$emit( eventName, […args] )

Parameters:

{string} eventName

[...args]

Trigger events on the current instance. Additional parameters are passed to the listener callback.

1. Parent components can use props to pass data to child components.

2. Subcomponents can use $emit to trigger custom events of parent components.

vm.$emit(event, arg) //Trigger events on the current instance

vm.$on(event, fn);//Run fn after listening to the event event;

Subcomponent

<template>  
  <div class="train-city">  
    <h3>父组件传给子组件的toCity:{{sendData}}</h3>   
    <br/><button @click=&#39;select(`大连`)&#39;>点击此处将‘大连’发射给父组件</button>  
  </div>  
</template>  
<script>  
  export default {  
    name:&#39;trainCity&#39;,  
    props:[&#39;sendData&#39;], // 用来接收父组件传给子组件的数据  
    methods:{  
      select(val) {  
        let data = {  
          cityname: val  
        };  
        this.$emit(&#39;showCityName&#39;,data);//select事件触发后，自动触发showCityName事件  
      }  
    }  
  }  
</script>

Parent component:

<template>  
    <div>父组件的toCity{{toCity}}</div>  
    <train-city @showCityName="updateCity" :sendData="toCity"></train-city>  
<template>  
<script>  
  import TrainCity from "./train-city";  
  export default {  
    name:&#39;index&#39;,  
    components: {TrainCity},  
    data () {  
      return {  
        toCity:"北京"  
      }  
    },  
    methods:{  
      updateCity(data){//触发子组件城市选择-选择城市的事件  
        this.toCity = data.cityname;//改变了父组件的值  
        console.log(&#39;toCity:&#39;+this.toCity)  
      }  
    }  
  }  
</script>

[Related recommendation: "vue.js Tutorial"]

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