JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://unpkg.com/vue@2.2.2/dist/vue.js"></script>
<div id="app">
<span v-for="(val, key, index) in person">{{key}}: {{val}}<span v-if="index !== last">, </span> </span>
</div>

JavaScript

new Vue({
  el: "#app",
  computed: {
    last(){
      return Object.keys(this.person).length-1;
    }
  },
  data:{
    person: {name: 'Joe', age: 35, department: 'IT'}
  }
});