Airline Check In

If you try to check in for your United return flight using the URL of your original United flight, you get the weirdest message.

United won’t allow you to check in when there’s more than 24 hours until your flight is scheduled to depart. I tried checking in about three days after my flight departed. I had already taken a United Airlines flight a few days before. I needed to check in for my return flight. My “smartphone” had the URL for the original flight in its history, so I just navigated to the check in page for the original flight, hoping that I could fill in my 6-character airline confirmation code.

Instead, I got a very confusing refusal to check in.

Try in NaN minute, at Invalid date Invalid date, Invalid date Invalid dateth

NaN stands for “Not A Number”. I can’t figure out where someone would divide by zero, or do x % 0 (x mod 0) in the case of figuring out minutes from an interval. The interval would be negative (slightly less than 3 days), but to get “minutes” from an interval, the divisor or the modulo would be 60, or maybe 3600. I bet the United programmers used NaN to mark an invalid, negative, interval, and it just propagated through to me, the user.

The “Invalid date Invalid date, Invalid date Invalid dateth” notation is a little more puzzling. “Invalid dateth” has to be the day-of-month, as in “20th” or “14th”. That would mean the current month should appear as the third “Invalid date”. Time-of-day and day-of-week fit for the first two “Invalid date” strings: “12:52” and “Wednesday” for example. That would make the whole thing “12:52 Wednesday, April 20th”.

It looks like United chose to validate any attempted check ins with JavaScript. It’s not clear to me if this is done in the browser or in the server. If it were me, I’d probably do a check in the browser for speed, but back it up with a server-side check for security.