JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.3/vue.min.js"></script>
<div id="app">
  <input v-model="user.firstName">
  <br>
  <input v-model="user.lastName">
  <pre>{{ user.fullName }}</pre>
  <pre>{{ user.getFullName() }}</pre>
  <pre>{{ user }}</pre>
  <button @click="onClick">click me</button>
</div>

JavaScript

class User {
  constructor(firstName, lastName) {
    this.firstName = firstName;
    this.lastName = lastName;
  }

  get fullName() {
    return this.firstName + ' ' + this.lastName;
  }

  getFullName() {
    return this.firstName + ' ' + this.lastName;
  }
}

new Vue({
  el: '#app',
  data: {
    user: new User('aaa', 'bbb'),
  },
  methods: {
    onClick() {
      console.log(this.user instanceof User);
    },
  },
});