JSFiddle - React, Tailwind, and code Playground
HTML
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.11/lodash.min.js"></script>
JavaScript
var oldArr = ['bold'];
var newArr = ['bold', 'italic'];
var diff = _.difference(newArr, oldArr);
console.log(diff);