function isValidDate(dateStr) {
// Checks for the following valid date formats:

// MM/DD/YY   MM/DD/YYYY   MM-DD-YY   MM-DD-YYYY
//var datePat = /^(\d{1,2})(\/|-)(\d{1,2})\2(\d{4})$/; // requires 4 digit year

//	Date Format: yyyy-MM-dd[ HH:mm:ss]
var datePat = /^(\d{4})(\/|-)(\d{1,2})\2(\d{1,2})( (\d{1,2})(\:)(\d{1,2})(\:)(\d{1,2}))?$/; // requires 4 digit year

var matchArray = dateStr.match(datePat); // is the format ok?
	if (matchArray == null) {
		return false;
	}
	year = matchArray[1];
	month = matchArray[3]; // parse date into variables
	day = matchArray[4];
	hour = matchArray[5];
	min = matchArray[7];
	sec = matchArray[9];

	if (month < 1 || month > 12) { // check month range
		return false;
	}
	if (day < 1 || day > 31) {
		return false;
	}
	if ((month==4 || month==6 || month==9 || month==11) && day==31) {
		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)) {
			return false;
			}
	}

	if(hour!='' && min!='' && sec!=''){
		//  if the "time" part is entered
		if (hour < 0 || hour > 23){
			return false;
		}
		if (min < 0 || min > 59){
			return false;
		}
		if (sec < 0 || sec > 59){
			return false;
		}
	}
	return true;
}