Reactive Dependency Tracking with `computed`

Explain dependency tracking by creating a reactive `computed` property that updates when its dependencies change.
    <title>Computed Example</title>
      #app {
        margin: 2rem;
    <div id="app">
      <input v-model="firstName" placeholder="First Name">
      <input v-model="lastName" placeholder="Last Name">
      <p>Full Name: {{ fullName }}</p>

    <script src=""></script>
      new Vue({
        el: '#app',
        data: {
          firstName: '',
          lastName: ''
        computed: {
          // computed property 'fullName' depending on 'firstName' and 'lastName'
          fullName: function() {
            return this.firstName + ' ' + this.lastName;
HTML with Vue.js: Input fields are bound to reactive data properties (firstName and lastName). A computed property (fullName) is declared which combines these and updates automatically when either dependency changes.