JavaScript Function Validate Date (valid date)

This function returns True if the passed text is a valid date, False if it is not.

/*

	ValidDate - true for valid date, false for invalid

*/

function IsValidDate(PossibleDate)

{

	var PDate = new String(PossibleDate);

	

	var regex = /(^\d{1,2})\/(\d{1,2})\/(\d{4,4})|(^\d{1,2})\/(\d{1,2})\/(\d{2,2})/;

	

	if( regex.test(PDate) )

	{

		var month = new String(RegExp.$1);

		var day = new String(RegExp.$2);

		var year = new String(RegExp.$3);

		if( month.length == 0 )

		{

			month = new String(RegExp.$4);

			day = new String(RegExp.$5);

			year = new String(RegExp.$6);

		}

		

		var today = new Date();

		var thisYear = new String(today.getFullYear());

		

		if( year.length == 2 )

		{					

			if( year > 50 )

			{

				year = String(Number(thisYear.substring(0,2))-1) + year;

			}

			else

			{

				year = thisYear.substring(0,2) + year;

			}

		}

		

		if( month < 1 || month > 12 ) { return false; }



		if( day < 1 || day > 31 ) { return false; }



		if ((month==4 || month==6 || month==9 || month==11) && day>30) { 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( (Number(year) < Number(thisYear) - 250) ||

			(Number(year) > Number(thisYear) + 250) )

			{ return false; }

			

		return true;

	}

	return false;

}