JSFiddle - React, Tailwind, and code Playground

HTML

start
<input class="start" />
<br/>end
<input class="end" />
<button value='calculate' class='hulk' >calculate</button>

JavaScript

$('.start,.end').datepicker();

$('.hulk').click(function () {
    var sDate = $('.start').val();
    var nDate = $('.end').val();

    console.log(sDate); /* Logs Date {Wed Oct 16 2013 00:00:00 GMT+0200 (CEST)} */
    console.log(nDate); /* Logs Date {Wed Oct 18 2013 00:00:00 GMT+0200 (CEST)} */
    var startdate = new Date(sDate);

    var enddate = new Date(nDate);

    enddate.setDate(enddate.getDate() - startdate.getDate());
    alert(monthDiff(startdate,enddate));
});


function monthDiff(d1, d2) {
    var months;
    months = (d2.getFullYear() - d1.getFullYear()) * 12;
    months -= d1.getMonth() + 1;
    months += d2.getMonth();
    return months <= 0 ? 0 : months;
}