Note: There is also a regular expression version available of this tip that can be used.

If you have any Domino forms where the user can input a date, the user can basically input whatever they want because the browser only knows of this field as a text field.

When the form gets submitted to the Domino server, the server will return an "Unable to Interpret Time or Date" error message if the date is invalid.

That's fine from an error standpoint since the form won't be saved, but it would be nice to prevent the form from being submitted if the date is invalid. That's where we wrote a JavaScript function to check if a passed date is valid.

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;
}

Copy this code and paste it into the JSHeader section of your form. To use this function you can put your own Submit button on the form and run some script behind the button to check the dates before actually submitting the form:

<input type=button value="Submit" onClick="verify(this.form)">

<script language="JavaScript"><!--
function verify(form) {
   dateFieldValue = form.DateField.value;
   if (checkValidDate(dateFieldValue)) {
      form.submit();
      return true;
   } else {
      alert("The date you supplied was invalid. Please try again.");
      return false;
   }
}
// -->
</script>

Alternately, you could have your field check for a valid date when exiting (use the onBlur javascript event). If you use this event, then you will not have to place your own submit button on the form -- the javascript event would trigger, even when submitting the form.