<template>
  <h2>Example expose Option</h2>
  <p>Only the 'message' data property is listed in the 'expose' option, so the 'createMessage' method from the child component is not available, and will not work:</p>
  <input type="text" v-model="inpText" placeholder="Write something">
  <button v-on:click="useMet">Use exposed method</button>
  <child-comp ref="childComp"/>
</template>

<script>
export default {
  data() {
    return {
      inpText: ''
    }
  },
  methods: {
    useMet() {
      this.$refs.childComp.createMessage(this.inpText);
    }
  },
  mounted() {
    this.$refs.childComp.message = 'Initial message!';
  }
}
</script>                  

<template>
  <div>
    <h3>ChildComp.vue</h3>
    <p>Message from parent component:</p>
    <p id="pEl">{{ message }}</p>
  </div>
</template>

<script>
export default {
  expose: ['message'],
  data() {
    return {
      message: ' '
    }
  },
  methods: {
    createMessage(msg) {
      this.message += msg + ' '
    }
  }
}
</script>

<style scoped>
div {
  border: solid black 1px;
  padding: 10px;
  max-width: 350px;
  margin-top: 20px;
}
#pEl {
  background-color: lightgreen;
  font-family: 'Courier New', Courier, monospace;
}
</style>                  

import { createApp } from 'vue'

import App from './App.vue'
import ChildComp from './components/ChildComp.vue'

const app = createApp(App)
app.component('child-comp', ChildComp)
app.mount('#app')