Regex Date + Time not working, but why?

Question

I have this following (working) regex, that checks for me, whether a string is a valid date:

(?:(?:(?:(?:(?:[1-9]\d)(?:0[48]|[2468][048]|[13579][26])|(?:(?:[2468][048]|[13579][26])00))(-)(?:0?2\1(?:29)))|(?:(?:[1-9]\d{3})(-)(?:(?:(?:0?[13578]|1[02])\2(?:31))|(?:(?:0?[13-9]|1[0-2])\2(?:29|30))|(?:(?:0?[1-9])|(?:1[0-2]))\2(?:0?[1-9]|1\d|2[0-8])))))

It works for a date that looks like this: 07.12.2017

Now I want to add, that the string also has a time which is check for correctness. I want 07.12.2017, 06:13 to be checked for validness.

I added to the former regex(above) this expression:

, ([0-1]?[0-9]|2[0-3]):[0-5][0-9]

But it doesn't work. Can anyone point out to me, what I did wrong?

What language are you using? What the context? By example if you are using Python you can do this without regex (and without tricky errors to fix) — Arount, Dec 20 '17 at 09:07
Don't use a regex for that! https://stackoverflow.com/q/7445328/171318 — hek2mgl, Dec 20 '17 at 09:11
I did: sap.ui.define([ "root/util/moment" ], function(moment) But it doesnt find any functions of moment, even though i see its attached to the window in the debugger — Madness, Dec 20 '17 at 09:48

KyleFairns · Answer 1 · 2017-12-20T11:56:51.627

Before I answer this, I would like to say that there are better ways to validate this, other than using regex, as February isn't a simple month to get right, some years it will have 28 days, others it will have 29 days, and it also isn't as simple as just "every four years February will have 29 days" either. The year 2100, you would expect to be a leap year under this pretext, but it is not, because it is not divisible by 400.

You're better off using an actual date library for this, as there are a lot of variables when it comes to the dates, that the regex will simply be a bad tool for.

With that out of the way, here is my answer:

(?:(?:(?:[0-2]\d)\.(?:0\d|1[12]))|(?:30\.(?:0[469]|11))|(?:3[01]\.(?:0[13578]|1[02])))\.\d+(?:, (?:[01]\d|2[0-4])\:[0-5]\d)?$

This should match dates in the format that you wish it to.

See it working on Regex101

Edit

I just did a bit of messing around with the regex to better provide functionality for this. This function will do a double check for leap years, and return a boolean for whether the date is valid or not.

function isValidDate(date) {
  let regex = /^(?:((?:[0-2]\d)\.(?:0\d|1[12]))|(30\.(?:0[469]|11))|(3[01]\.(?:0[13578]|1[02])))\.(\d+)(?:, (?:[01]\d|2[0-4])\:[0-5]\d)?$/,
    matches = date.match(regex);

  if (!matches) {
    return false;
  }

  let dayMonth = matches[1] || matches[2] || matches[3],
    year = matches[4],
    valid = !dayMonth || !year ? false : true;

  if (dayMonth == "29.02") {
    let divisibleBy = {four: year % 4 === 0, oneHundred: year % 100 === 0, fourHundred: year % 400 === 0 };
    if (year > 400) {
      if (!divisibleBy.four) {
        valid = false;
      }
      if (divisibleBy.four && divisibleBy.oneHundred && !divisibleBy.fourHundred) {
        valid = false;
      }
    }
  }
  return valid;
}

console.log(
  isValidDate("29.02.2100"),
  isValidDate("29.02.2000"),
  isValidDate("25.12.2017, 22:00"),
  isValidDate("31.05.1678"),
  isValidDate("32.05.1900"),
  isValidDate("29.02.32000, 06:15")
)

Regex Date + Time not working, but why?

1 Answers1