<template>
  <h1>Add/Remove &lt;p&gt; Tag</h1>
  <button @click="this.exists = !this.exists">{{btnText}}</button><br>
  <p v-if="exists">Hello World!</p>
</template>

<script>
export default {
  data() {
    return {
      exists: false
    }
  },
  computed: {
    btnText() {
      if(this.exists) {
        return 'Remove';
      }
      else {
        return 'Add';
      }
    }
  }
}
</script>

<style>
  p {
    background-color: lightgreen;
    display: inline-block;
    padding: 10px;
  }
</style>                  

import { createApp } from 'vue'

import App from './App.vue'

const app = createApp(App)
app.mount('#app')