javascript difference between two dates in days
/* difference between date1 and date2 in days (date2 - date1) */
/* date1 and date 2 are already javascript date objects */
function dateDifference(date2, date1) {
const _MS_PER_DAY = 1000 * 60 * 60 * 24;
// Discard the time and time-zone information.
const utc1 = Date.UTC(date1.getFullYear(), date1.getMonth(), date1.getDate());
const utc2 = Date.UTC(date2.getFullYear(), date2.getMonth(), date2.getDate());
return Math.floor((utc2 - utc1) / _MS_PER_DAY);
}