date difference
function daysBetween(first, second) {
// Copy date parts of the timestamps, discarding the time parts.
var one = new Date(first.getFullYear(), first.getMonth(), first.getDate());
var two = new Date(second.getFullYear(), second.getMonth(), second.getDate());
// Do the math.
var millisecondsPerDay = 1000 * 60 * 60 * 24;
var millisBetween = two.getTime() - one.getTime();
var days = millisBetween / millisecondsPerDay;
// Round down.
return Math.floor(days);
// it will return date difference in days
}