function checkValidDate(dateStr) {
// dateStr must be of format month day year with either slashes
// or dashes separating the parts. Some minor changes would have
// to be made to use day month year or another format.
// This function returns True if the date is valid.
var slash1 = dateStr.indexOf("/");
if (slash1 == -1) { slash1 = dateStr.indexOf("-"); }
// if no slashes or dashes, invalid date
if (slash1 == -1) { return false; }
var dateMonth = dateStr.substring(0, slash1)
var dateMonthAndYear = dateStr.substring(slash1+1, dateStr.length);
var slash2 = dateMonthAndYear.indexOf("/");
if (slash2 == -1) { slash2 = dateMonthAndYear.indexOf("-"); }
// if not a second slash or dash, invalid date
if (slash2 == -1) { return false; }
var dateDay = dateMonthAndYear.substring(0, slash2);
var dateYear = dateMonthAndYear.substring(slash2+1, dateMonthAndYear.length);
if ( (dateMonth == "") || (dateDay == "") || (dateYear == "") ) { return false; }
// if any non-digits in the month, invalid date
for (var x=0; x < dateMonth.length; x++) {
var digit = dateMonth.substring(x, x+1);
if ((digit < "0") || (digit > "9")) { return false; }
}
// convert the text month to a number
var numMonth = 0;
for (var x=0; x < dateMonth.length; x++) {
digit = dateMonth.substring(x, x+1);
numMonth *= 10;
numMonth += parseInt(digit);
}
if ((numMonth <= 0) || (numMonth > 12)) { return false; }
// if any non-digits in the day, invalid date
for (var x=0; x < dateDay.length; x++) {
digit = dateDay.substring(x, x+1);
if ((digit < "0") || (digit > "9")) { return false; }
}
// convert the text day to a number
var numDay = 0;
for (var x=0; x < dateDay.length; x++) {
digit = dateDay.substring(x, x+1);
numDay *= 10;
numDay += parseInt(digit);
}
if ((numDay <= 0) || (numDay > 31)) { return false; }
// February can't be greater than 29 (leap year calculation comes later)
if ((numMonth == 2) && (numDay > 29)) { return false; }
// check for months with only 30 days
if ((numMonth == 4) || (numMonth == 6) || (numMonth == 9) || (numMonth == 11)) {
if (numDay > 30) { return false; }
}
// if any non-digits in the year, invalid date
for (var x=0; x < dateYear.length; x++) {
digit = dateYear.substring(x, x+1);
if ((digit < "0") || (digit > "9")) { return false; }
}
// convert the text year to a number
var numYear = 0;
for (var x=0; x < dateYear.length; x++) {
digit = dateYear.substring(x, x+1);
numYear *= 10;
numYear += parseInt(digit);
}
// Year must be a 2-digit year or a 4-digit year
if ( (dateYear.length != 2) && (dateYear.length != 4) ) { return false; }
// if 2-digit year, use 50 as a pivot date
if ( (numYear < 50) && (dateYear.length == 2) ) { numYear += 2000; }
if ( (numYear < 100) && (dateYear.length == 2) ) { numYear += 1900; }
if ((numYear <= 0) || (numYear > 9999)) { return false; }
// check for leap year if the month and day is Feb 29
if ((numMonth == 2) && (numDay == 29)) {
var div4 = numYear % 4;
var div100 = numYear % 100;
var div400 = numYear % 400;
// if not divisible by 4, then not a leap year so Feb 29 is invalid
if (div4 != 0) { return false; }
// at this point, year is divisible by 4. So if year is divisible by
// 100 and not 400, then it's not a leap year so Feb 29 is invalid
if ((div100 == 0) && (div400 != 0)) { return false; }
}
// date is valid
return true;
}