SOURCE

Vue.component('parent-component',{
  template: `
		<div>
			{{ title }}
			<br/>
			<child-component @updateParent="update">
      </child-component>
		</div>
	`,
  data(){
    return {
      title: "父组件"
    }
  },
  methods: {
    update(){
      this.title = "父组件更新了";
    },
  },
  created(){
    this.$on("updateParent",()=>{
      console.log('这里不会执行');
    });
  }
});
Vue.component('child-component',{
  template: `
		<div>
			{{ title }}
			<br/>
      <button @click="updateByEmit">
         通过 $emit 更新父组件
      </button>
		</div>
	`,
  data(){
    return {
      title: "子组件"
    }
  },
  methods: {
    updateByEmit(){
      this.$emit("updateParent");
    },
  },
  created(){
    this.$on("updateParent",()=>{
      this.title = "子组件也更新了"
    });
  }
});

new Vue({
  el: '#root',
})

<script src="https://unpkg.com/vue"></script>

<div id="root">
  <parent-component>
  </parent-component>
</div>