JSFiddle - React, Tailwind, and code Playground

HTML

<div id="app">
<div 
  v-for="(val, index) in array"
  :class="['a'+index, index === 1 ? 'b' : '']">
    {{ val }}
</div>
<div 
  v-for="(val, index) in array"
  :class="['a'+index, {b: index === 1}]">
    {{ val }}
</div>
</div>

JavaScript

new Vue({
  el: '#app',
  data: {
    array: [1, 2, 3, 4, 5]
  },
});