regex - javascript regexp, validating date problem

Question

I have some code for validating date below:

function validateForm() {
var errFound = 0;       
//var patt_date = new RegExp("^((((19|20)(([02468][048])|([13579][26]))-02-29))|((20[0-9][0-9])|(19[0-9][0-9]))-((((0[1-9])|(1[0-2]))-((0[1-9])|(1d)|(2[0-8])))|((((0[13578])|(1[02]))-31)|(((0[1,3-9])|(1[0-2]))-(29|30)))))$");
var patt_date = new RegExp("^[0-9]{4}-(((0[13578]|(10|12))-(0[1-9]|[1-2][0-9]|3[0-1]))|(02-(0[1-9]|[1-2][0-9]))|((0[469]|11)-(0[1-9]|[1-2][0-9]|30)))$");
if (patt_date.test(document.getElementById("datefrom").value) == false){errFound = errFound + 1;document.getElementById("datefrom").className = "error";}

if (errFound > 0)
    alert('Please correct red colored field!');
else
    return true;
return false;   
}

Above code should work with YYYY-MM-DD format, but fail to validate date such as "2009-02-29"

The commented code should work (//var patt_date = new RegExp...), it can catch "2009-02-29",
but it ruin the validation when i put invalid data and try to correct it, it keeps complain there something wrong with form value after i had correct them (especially on form with multiple input)

Maybe someone can fix the current regex?

---

Edited, what i want just a simple replacement for above regexp, mean a new regexp pattern not the whole new method to validate date
And for reference, i simply grab the regexp pattern from:
http://www.regexlib.com/REDetails.aspx?regexp_id=694 and
http://www.regexlib.com/REDetails.aspx?regexp_id=933

Tested with 2009-02-29, 1st link work & 2nd not. Again the problem was only the 2nd regexp didn't detect value 2009-02-29 as invalid while 1st can (but it ruin my code? so it's must be there something wrong with it).

Thanks,
Dels

Answer 1

Don't do the whole date validation with a regular expression, that's really pushing the limits of what regexps were designed for. I would suggest this procedure instead:

1. Check date against regexp /^d{4}-d{2}-d{2}$/
2. Extract year, month, and day using substr() and convert to integers
3. Use some if statements to validate the integers. Like so:

    if (month == 2) {
        if (day == 29) {
            if (year % 4 != 0 || year % 100 == 0 && year % 400 != 0) {
                // fail
            }
        }
        else if (day > 28) {
            // fail
        }
    }
    else if (month == 4 || month == 6 || month  == 9 || month == 11) {
        if (day > 30) {
            // fail
        }
    }
    else {
        if (day > 31) {
            // fail
    }

(That could certainly be written more concisely) Alternatively, you could probably perform this validation using Javascript's Date class - you might have to do something like parsing the date, converting it back to a string, and checking if the two strings are equal. (I'm not a Javascript expert)