Edit in JSFiddle

<div id="app">
 <p style="white-space: pre-line;">{{ message }}</p>
 <textarea v-model="message" placeholder="add multiple lines"></textarea>
</div>
<script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
var app = new Vue({
  el: '#app',
  data: {
    message: "Hello YouTube!"
  }
})