Javascript Date Validation / Comparison

Problem:
User enters two dates, say start date and end date, then we need to alert him if the start date is greater than end date.

Solution:
Assume we are getting the date to the input field using a datepicker.

First we have to convert the string into Date() object using
var dObj = new Date(year, month, date); (also note: the month value range from 0 to 11)
and we can compare the dates.

Example:
var x = document.formName;

//assume the date format is YYYY/MM/DD
var sDate1 = x.start_date.value;
var sDate = new Date(sDate1.split('/')[0], parseInt((sDate1.split('/')[1])-1), sDate1.split('/')[2]);
var eDate1 = x.end_date.value;
var eDate = new Date(eDate1.split('/')[0], parseInt((eDate1.split('/')[1])-1), eDate1.split('/')[2]);
if(eDate >= sDate)
{
    alert("End date is greater than start date; please try again....");
    return false;
}

-

How to add month, days, years in a date

<?php
$day1 = "2008/10/20";

//add month
$day2 = date("Y/m/d", strtotime("+2 months", strtotime($day1)));
//"2008/12/20"
$day2 = date("Y/m/d", strtotime("+3 months", strtotime($day1)));
//"2009/01/20"
//add days
$day2 = date("Y/m/d", strtotime("+5 days", strtotime($day1))); //"2008/10/25"
$day2 = date("Y/m/d", strtotime("+20 days", strtotime($day1))); //"2008/11/09"
//years
$day2 = date("Y/m/d", strtotime("+2 years", strtotime($day1))); //"2010/10/20"
?>
Also we can add weeks.