Date Validation for Holidays and Working days

<script language = "Javascript">
 
var dtCh= "/";
var minYear=1900;
var maxYear=2100;
 
function isInteger(s){
	var i;
    for (i = 0; i < s.length; i++){   
        // Check that current character is number.
        var c = s.charAt(i);
        if (((c < "0") || (c > "9"))) return false;
    }
    // All characters are numbers.
    return true;
}
 
function stripCharsInBag(s, bag){
	var i;
    var returnString = "";
    // Search through string's characters one by one.
    // If character is not in bag, append to returnString.
    for (i = 0; i < s.length; i++){   
        var c = s.charAt(i);
        if (bag.indexOf(c) == -1) returnString += c;
    }
    return returnString;
}
 
function daysInFebruary (year){
	// February has 29 days in any year evenly divisible by four,
    // EXCEPT for centurial years which are not also divisible by 400.
    return (((year % 4 == 0) && ( (!(year % 100 == 0)) || (year % 400 == 0))) ? 29 : 28 );
}
function DaysArray(n) {
	for (var i = 1; i <= n; i++) {
		this[i] = 31
		if (i==4 || i==6 || i==9 || i==11) {this[i] = 30}
		if (i==2) {this[i] = 29}
   } 
   return this
}
 
function isDate(dtStr){
	var daysInMonth = DaysArray(12)
	var pos1=dtStr.indexOf(dtCh)
	var pos2=dtStr.indexOf(dtCh,pos1+1)
	var strMonth=dtStr.substring(0,pos1)
	var strDay=dtStr.substring(pos1+1,pos2)
	var strYear=dtStr.substring(pos2+1)
	strYr=strYear
	if (strDay.charAt(0)=="0" && strDay.length>1) strDay=strDay.substring(1)
	if (strMonth.charAt(0)=="0" && strMonth.length>1) strMonth=strMonth.substring(1)
	for (var i = 1; i <= 3; i++) {
		if (strYr.charAt(0)=="0" && strYr.length>1) strYr=strYr.substring(1)
	}
	month=parseInt(strMonth)
	day=parseInt(strDay)
	year=parseInt(strYr)
	if (pos1==-1 || pos2==-1){
		alert("The date format should be : mm/dd/yyyy")
		return false
	}
	if (strMonth.length<1 || month<1 || month>12){
		alert("Please enter a valid month")
		return false
	}
	if (strDay.length<1 || day<1 || day>31 || (month==2 && day>daysInFebruary(year)) || day > daysInMonth[month]){
		alert("Please enter a valid day")
		return false
	}
	if (strYear.length != 4 || year==0 || year<minYear || year>maxYear){
		alert("Please enter a valid 4 digit year between "+minYear+" and "+maxYear)
		return false
	}
	if (dtStr.indexOf(dtCh,pos2+1)!=-1 || isInteger(stripCharsInBag(dtStr, dtCh))==false){
		alert("Please enter a valid date")
		return false
	}
	var dateVar = new Date(year,month,day) // (Year, Month, Date)
	alert("DATE :" + dateVar.getDate());
	alert("DAY :" + dateVar.getDay());
	alert("MONTH :" + dateVar.getMonth());
	alert("YEAR :" + dateVar.getYear());
	check_holiday(dateVar);
return true
}
 
function ValidateDate(){
	var dt=document.getElementById('txtDate');
	if (isDate(dt.value)==false){
		dt.focus()
		return false
	}
    return true
 }
 
 
function check_holiday (dt_date) {
	// check simple dates (month/date - no leading zeroes)
	var n_date = dt_date.getDate(),
		n_month = dt_date.getMonth() + 1;
	var s_date1 = n_month + '/' + n_date;
		
	if (   s_date1 == '1/1'   // New Year's Day
		|| s_date1 == '8/15'   // Independence Day
		|| s_date1 == '12/25' // Christmas Day
	) return true;
	
	// weekday from beginning of the month (month/num/day)
	var n_wday = dt_date.getDay(),
		n_wnum = Math.floor((n_date - 1) / 7) + 1;
	var s_date2 = n_month + '/' + n_wnum + '/' + n_wday;
	
	if (   s_date2 == '1/3/1'  // Birthday of Martin Luther King, third Monday in January
		|| s_date2 == '2/3/1'  // Washington's Birthday, third Monday in February
		|| s_date2 == '5/3/6'  // Armed Forces Day, third Saturday in May
		|| s_date2 == '9/1/1'  // Labor Day, first Monday in September
		|| s_date2 == '10/2/1' // Columbus Day, second Monday in October
		|| s_date2 == '11/4/4' // Thanksgiving Day, fourth Thursday in November
	) return true;
 
	// weekday number from end of the month (month/num/day)
	var dt_temp = new Date (dt_date);
	dt_temp.setDate(1);
	dt_temp.setMonth(dt_temp.getMonth() + 1);
	dt_temp.setDate(dt_temp.getDate() - 1);
	n_wnum = Math.floor((dt_temp.getDate() - n_date - 1) / 7) + 1;
	var s_date3 = n_month + '/' + n_wnum + '/' + n_wday;
	
	if (   s_date3 == '5/1/1'  // Memorial Day, last Monday in May
	) return true;
 
	// misc complex dates
	if (s_date1 == '1/20' && (((dt_date.getFullYear() - 1937) % 4) == 0) 
	// Inauguration Day, January 20th every four years, starting in 1937. 
	) return true;
		
	if (n_month == 11 && n_date >= 2 && n_date < 9 && n_wday == 2
	// Election Day, Tuesday on or after November 2. 
	) return true;
	
	return false;
}
</script>
 
<html>
<form >
                <p>Enter a Date <font color="#CC0000"><b>(mm/dd/yyyy)</b></font> 
                  : 
                  <input type="text" name="txtDate" maxlength="10" size="15">
                </p>
                <p> 
                  <input type="button" name="OK" value="OK" onclick="ValidateDate()">
                </p>
 
				
 
              </form>
</html>