child.vue

<template>
       <div>
           <p>hello world</p>
           <button @click = "go" class="btn btn-success">go</button>
       </div>
</template>


<script lang="ts">
import Vue from 'vue'
import {defineComponent} from "vue"
export default defineComponent({
    emits:['haha'],
   setup(prop,context){
       const methods = {
           go(){
               context.emit("haha")
           }
       }
       return {
           ...methods
       }
   } 
})
</script>

<style>

</style>

App.vue  使用就行了