Q1 How do you check if a date is valid?

<script language="JavaScript"><!--
function y2k(number) { return (number < 1000) ? number + 1900 : number; }

function isDate (day,month,year) {
// checks if date passed is valid
// will accept dates in following format:
// isDate(dd,mm,ccyy), or
// isDate(dd,mm) - which defaults to the current year, or
// isDate(dd) - which defaults to the current month and year.
// Note, if passed the month must be between 1 and 12, and the
// year in ccyy format.

    var today = new Date();
    year = ((!year) ? y2k(today.getYear()):year);
    month = ((!month) ? today.getMonth():month-1);
    if (!day) return false
    var test = new Date(year,month,day);
    if ( (y2k(test.getYear()) == year) &&
         (month == test.getMonth()) &&
         (day == test.getDate()) )
        return true;
    else
        return false
}

if (isDate(31,2,1997))
    document.write("Valid");
else
    document.write("Invalid");
//--></script>

var myDate = new Date();
alert(formatDate(myDate, "ww, mmmm, d, yy"));

<script language="JavaScript"><!--
//**************************************************************************************
//        Name: formatDate
//
// Description: Formats a date using a format string.
//              d or dd represents the day of the month (eg 1 or 01)
//              m or mm represents the month as a number (eg 1 or 01)
//              mmm or mmmm represents the month as a string (eg Jan or January)
//              y or yy represents the year (eg 99 or 1999)
//              w or ww represents the day of the week (eg Mon or Monday)
//              example: formatDate(myDate, "mm/dd/yy") might look like 01/01/2000
//  Parameters: strFullDate - required - the date to display (a date object)
//          strFormatString - required - a format string
//
//**************************************************************************************
function formatDate(strFullDate, strFormatString) {

 var strMonths = new Array();
 var strDay = new Array();

 strMonths[0]  = "January";
 strMonths[1]  = "February";
 strMonths[2]  = "March";
 strMonths[3]  = "April";
 strMonths[4]  = "May";
 strMonths[5]  = "June";
 strMonths[6]  = "July";
 strMonths[7]  = "August";
 strMonths[8]  = "September";
 strMonths[9]  = "October";
 strMonths[10] = "November";
 strMonths[11] = "December";

 strDay[0]  = "Sunday";
 strDay[1]  = "Monday";
 strDay[2]  = "Tuesday";
 strDay[3]  = "Wednesday";
 strDay[4]  = "Thursday";
 strDay[5]  = "Friday";
 strDay[6]  = "Saturday";

 var strValue_d    = strFullDate.getDate();
 var strValue_dd   = (strValue_d < 10) ? '0' + strValue_d : strValue_d;
 var strValue_m    = strFullDate.getMonth() + 1;
 var strValue_mm   = (strValue_m < 10) ? '0' + strValue_m : strValue_m;
 var strValue_mmmm = strMonths[strFullDate.getMonth()];
 var strValue_mmm  = strValue_mmmm.substr(0,3);
 var strValue_yy   = strFullDate.getYear() + 1900 + "";
 var strValue_y    = strValue_yy.substr(2,2);
 var strValue_ww   = strDay[strFullDate.getDay()];
 var strValue_w    = strValue_ww.substr(0,3);

 if (strFormatString.indexOf("dd") > -1) {
  strFormatString = strFormatString.replace("dd", "strValue_dd");
 }
 else {
  if (strFormatString.indexOf("d") > -1) {
   strFormatString = strFormatString.replace("d", "strValue_d");
  }
 }

 if (strFormatString.indexOf("mmmm") > -1) {
  strFormatString = strFormatString.replace("mmmm", "strValue_mmmm");
 }
 else {
  if (strFormatString.indexOf("mmm") > -1) {
   strFormatString = strFormatString.replace("mmm", "strValue_mmm");
  }
  else {
   if (strFormatString.indexOf("mm") > -1) {
    strFormatString = strFormatString.replace("mm", "strValue_mm");
   }
   else {
    if (strFormatString.indexOf("m") > -1) {
     strFormatString = strFormatString.replace("m", "strValue_m");
    }
   }
  }
 }

 if (strFormatString.indexOf("yy") > -1) {
  strFormatString = strFormatString.replace("yy", "strValue_yy");
 }
 else {
  if (strFormatString.indexOf("y") > -1) {
   strFormatString = strFormatString.replace("y", "strValue_y");
  }
 }

 if (strFormatString.indexOf("ww") > -1) {
  strFormatString = strFormatString.replace("ww", "strValue_ww");
 }
 else {
  if (strFormatString.indexOf("w") > -1) {
   strFormatString = strFormatString.replace("w", "strValue_w");
  }
 }

 strFormatString = strFormatString.replace("strValue_dd", strValue_dd);
 strFormatString = strFormatString.replace("strValue_d", strValue_d);
 strFormatString = strFormatString.replace("strValue_mmmm", strValue_mmmm);
 strFormatString = strFormatString.replace("strValue_mmm", strValue_mmm);
 strFormatString = strFormatString.replace("strValue_mm", strValue_mm);
 strFormatString = strFormatString.replace("strValue_m", strValue_m);
 strFormatString = strFormatString.replace("strValue_yy", strValue_yy);
 strFormatString = strFormatString.replace("strValue_y", strValue_y);
 strFormatString = strFormatString.replace("strValue_ww", strValue_ww);
 strFormatString = strFormatString.replace("strValue_w", strValue_w);

 return strFormatString;
}
//--></script>