Get Date Difference in Days between Two Dates

<script type="text/javascript">
    function daysBetween(startDate, endDate) {
        var millisecondsPerDay = 1000 * 60 * 60 * 24;
        var startDateUTC = Date.UTC(startDate.getFullYear(), startDate.getMonth(), startDate.getDate());
        var endDateUTC = Date.UTC(endDate.getFullYear(), endDate.getMonth(), endDate.getDate());

        return Math.floor((endDateUTC - startDateUTC) / millisecondsPerDay);
    }
</script>