JSFiddle - React, Tailwind, and code Playground

HTML

<p id="res"></p>
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.9.0/moment.min.js"></script>

JavaScript

var a = moment('1/1/2012', 'DD/MM/YYYY');
var b = moment('1/1/2013', 'DD/MM/YYYY');
var days = b.diff(a, 'days');

$('#res').text(days);