function isValidDate(dateStr) {
// Checks for the following valid date formats:
// MM/DD/YY   MM/DD/YYYY   MM-DD-YY   MM-DD-YYYY
// Also separates date into month, day, and year variables
// To require a 4 digit year entry, use this line instead:
var datePat = /^(\d{1,2})(\/|-)(\d{1,2})\2(\d{4})$/;
var matchArray = dateStr.match(datePat); // is the format ok?
if (matchArray == null) 
{
	return false;
}
month = matchArray[1]; // parse date into variables
day = matchArray[3];
year = matchArray[4];
if (month < 1 || month > 12) 
{ // check month range
	alert("Month must be between 1 and 12.");
	return false;
}
if (day < 1 || day > 31) 
{
	alert("Day must be between 1 and 31.");
	return false;
}
if ((month==4 || month==6 || month==9 || month==11) && day==31)
{
	alert("Month "+month+" doesn't have 31 days!")
	return false
}
if (month == 2)
{ // check for february 29th
	var isleap = (year % 4 == 0 && (year % 100 != 0 || year % 400 == 0));
	if (day>29 || (day==29 && !isleap))
	{
		alert("February " + year + " doesn't have " + day + " days!");
		return false;
	}
}
return true;  // date is valid
}