javascript date validation not validation February 31

Question

I am trying to write some code with will validate form data. I have a date field which should have a mm/dd/yyyy format. I needed to catch exceptions such as February 31, so I added this code:

var d = new Date(dob);
if (isNaN(d.getTime())) { //this if is to take care of February 31, BUT IT DOESN'T!
  error = 1;
  message += "<li>Invalid Date</li>";
} else {
  var date_regex = /^(0[1-9]|1[0-2])/(0[1-9]|1d|2d|3[01])/(19|20)d{2}$/;
  var validFormat = date_regex.test(dob);
  if (!(validFormat)) {
    error = 1;
    message += "<li>Invalid date format - date must have format mm/dd/yyyy</li>";
  }
}

However I found something very weird: while the date 02/32/2000 errors as an invalid date, 02/31/2000 does not!

Answer 1

Due to what I said in the comments...

Another way you could check if a date is valid is by checking whether or not the stuff you passed into the new Date function is the same as what comes out of it, like this:

// Remember that the month is 0-based so February is actually 1...
function isValidDate(year, month, day) {
    var d = new Date(year, month, day);
    if (d.getFullYear() == year && d.getMonth() == month && d.getDate() == day) {
        return true;
    }
    return false;
}

then you could do this:

if (isValidDate(2013,1,31))

and it would return true if valid and false if invalid.