vue 3 emit warning “ Extraneous non-emits event listeners”

问题

I am trying to emit data from child to parent using the composition API

I get the following warning.

[Vue warn]: Extraneous non-emits event listeners (updatedcount) were passed to component but could not be automatically inherited because component renders fragment or text root nodes. If the listener is intended to be a component custom event listener only, declare it using the "emits" option.at <HelloWorld onUpdatedcount=fn > at

childcomponent.vue

<template>
  <h1>{{ store.count }}</h1>
  <button @click="fired">click me</button>
</template>

<script>
import useStore from "../store/store.js";
export default {
  name: "HelloWorld",
  setup(_,{ emit }) {
    const store = useStore();

    const fired = () => {
      store.count++;
      emit("updatedcount", store.count);
    };

    return {
      store,
      fired
    };
  },
};
</script>

parentcomponent.vue

<template>
  <div>
    {{ hello }}
    <br />
    <br />
    <input type="text" v-model="hello.searchQuery" />
    <br><br>
    <button @click="hello.count--">click me too!</button>
    <hello-world @updatedcount="mydata" />
  </div>
</template>

<script>
import HelloWorld from "./components/HelloWorld.vue";
import useStore from "./store/store.js";

export default {
  components: {
    HelloWorld,
  },
  setup() {
    const hello = useStore();

    function mydata(event) {
      console.log(event);
    }

    return {
      hello,
      mydata
    };
  },
};
</script>

回答1:

I think you'll need to define the emits in your component: https://v3.vuejs.org/guide/component-custom-events.html#defining-custom-events

export default {
  name: "HelloWorld",
  emits: ["updatedcount"],// this line
  setup(_,{ emit }) {
    const store = useStore();

    const fired = () => {
      store.count++;
      emit("updatedcount", store.count);
    };

    return {
      store,
      fired
    };
  },
};

According documentation you could even validate the event by checking if the parameter is available.

来源：https://stackoverflow.com/questions/64220737/vue-3-emit-warning-extraneous-non-emits-event-listeners