jQuery addClass example

Change class name on click in jQuery

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.24.0/moment.min.js"></script>
<input type="text" id="date" placeholder="2020-08-27">

JavaScript

var value = 0;
var now = new Date();
$("#date").on("change", function() {
   var value = $(this).val();
   var future = new Date(value);
   var diff = moment(future).diff(moment(now), 'month');
   console.log(diff);
});