Is the regex returning the correct result?

Question

Is the regex returning the correct result?

I need to discuss the date field with a format of YYYYMMDD, as shown below:

zod.string().max(8).regex(new RegExp('^(19[0-9][0-9]|20[0-9][0-9]|[0-1][0-9]{3})(1[0-2]|0[1-9])(3[01]|[0-2][1-9]|[12]0)$'));

The value provided is 20001915.

The definition seems correct, however when tested on an online checker (https://www.regextester.com/[enter link description here]1) it shows FALSE (due to incorrect month number - 19). Surprisingly, zod still considers this value as correct. I am wondering why?

regex typescript zod

Answer 1

Answer №1

One comment pointed out that the regular expression is correct, but it's essential to understand that while the regex checks the format, it doesn't validate the date itself for accuracy in real-world terms. For instance, "20001915" follows the correct format (YYYYMMDD), but it signifies the 19th month, which isn't valid. Therefore, an external online checker correctly identifies it as FALSE.

To ensure the date's validity, you can validate it separately using the following code snippet:

const dateString = "20001915";
const year = parseInt(dateString.substring(0, 4));
const month = parseInt(dateString.substring(4, 6)) - 1; // Months are 0-indexed
const day = parseInt(dateString.substring(6, 8));

const date = new Date(year, month, day);

if (
  date.getFullYear() === year &&
  date.getMonth() === month &&
  date.getDate() === day
) {
  console.log("Valid date.");
} else {
  console.log("Invalid date.");
}

Additionally, you can optimize the regex pattern like so:

^(19\d\d|20\d\d)(0[1-9]|1[0-2])(0[1-9]|[12][0-9]|3[01])$

Answer 2

One comment pointed out that the regular expression is correct, but it's essential to understand that while the regex checks the format, it doesn't validate the date itself for accuracy in real-world terms. For instance, "20001915" follows the correct format (YYYYMMDD), but it signifies the 19th month, which isn't valid. Therefore, an external online checker correctly identifies it as FALSE.

To ensure the date's validity, you can validate it separately using the following code snippet:

const dateString = "20001915";
const year = parseInt(dateString.substring(0, 4));
const month = parseInt(dateString.substring(4, 6)) - 1; // Months are 0-indexed
const day = parseInt(dateString.substring(6, 8));

const date = new Date(year, month, day);

if (
  date.getFullYear() === year &&
  date.getMonth() === month &&
  date.getDate() === day
) {
  console.log("Valid date.");
} else {
  console.log("Invalid date.");
}

Additionally, you can optimize the regex pattern like so:

^(19\d\d|20\d\d)(0[1-9]|1[0-2])(0[1-9]|[12][0-9]|3[01])$

Is the regex returning the correct result?

Answer №1

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