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How to check if a string is a valid date using regular expression or regex in JavaScript?

MELVIN GEORGE
Hi, I'm Melvin George, A web developer, and a blogger.
Originally published at melvingeorge.me ・3 min read

Originally posted here!

To check if a string is a valid date using regex in JavaScript, we can use a regex expression to match the symbols like /, ., - and the numbers in between them in the format of dd/mm/yyyy , dd-mm-yyyy or dd.mm.yyyy.

TL;DR

// Regular expression to check if string is valid date
const regexExp = /(?:(?:31(\/|-|\.)(?:0?[13578]|1[02]))\1|(?:(?:29|30)(\/|-|\.)(?:0?[13-9]|1[0-2])\2))(?:(?:1[6-9]|[2-9]\d)?\d{2})$|^(?:29(\/|-|\.)0?2\3(?:(?:(?:1[6-9]|[2-9]\d)?(?:0[48]|[2468][048]|[13579][26])|(?:(?:16|[2468][048]|[3579][26])00))))$|^(?:0?[1-9]|1\d|2[0-8])(\/|-|\.)(?:(?:0?[1-9])|(?:1[0-2]))\4(?:(?:1[6-9]|[2-9]\d)?\d{2})/gi;

// String with valid date separated by dash
const str = "01-01-2021";

regexExp.test(str); // true
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First let's see the regular expression which we will use to match the strings. It can be done like this,

// Regular expression to check if string is valid date
const regexExp = /(?:(?:31(\/|-|\.)(?:0?[13578]|1[02]))\1|(?:(?:29|30)(\/|-|\.)(?:0?[13-9]|1[0-2])\2))(?:(?:1[6-9]|[2-9]\d)?\d{2})$|^(?:29(\/|-|\.)0?2\3(?:(?:(?:1[6-9]|[2-9]\d)?(?:0[48]|[2468][048]|[13579][26])|(?:(?:16|[2468][048]|[3579][26])00))))$|^(?:0?[1-9]|1\d|2[0-8])(\/|-|\.)(?:(?:0?[1-9])|(?:1[0-2]))\4(?:(?:1[6-9]|[2-9]\d)?\d{2})/gi;
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This would match for date strings in the format of dd/mm/yyyy , dd-mm-yyyy or dd.mm.yyyy.

Now let's write a string with valid date like this,

// Regular expression to check if string is valid date
const regexExp = /(?:(?:31(\/|-|\.)(?:0?[13578]|1[02]))\1|(?:(?:29|30)(\/|-|\.)(?:0?[13-9]|1[0-2])\2))(?:(?:1[6-9]|[2-9]\d)?\d{2})$|^(?:29(\/|-|\.)0?2\3(?:(?:(?:1[6-9]|[2-9]\d)?(?:0[48]|[2468][048]|[13579][26])|(?:(?:16|[2468][048]|[3579][26])00))))$|^(?:0?[1-9]|1\d|2[0-8])(\/|-|\.)(?:(?:0?[1-9])|(?:1[0-2]))\4(?:(?:1[6-9]|[2-9]\d)?\d{2})/gi;

// String with valid date separated by dash
const str = "01-01-2021";
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Now to test the string, we can use the test() method available in the regular expression we defined. It can be done like this,

// Regular expression to check if string is valid date
const regexExp = /(?:(?:31(\/|-|\.)(?:0?[13578]|1[02]))\1|(?:(?:29|30)(\/|-|\.)(?:0?[13-9]|1[0-2])\2))(?:(?:1[6-9]|[2-9]\d)?\d{2})$|^(?:29(\/|-|\.)0?2\3(?:(?:(?:1[6-9]|[2-9]\d)?(?:0[48]|[2468][048]|[13579][26])|(?:(?:16|[2468][048]|[3579][26])00))))$|^(?:0?[1-9]|1\d|2[0-8])(\/|-|\.)(?:(?:0?[1-9])|(?:1[0-2]))\4(?:(?:1[6-9]|[2-9]\d)?\d{2})/gi;

// String with valid date separated by dash
const str = "01-01-2021";

regexExp.test(str); // true
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  • The test() method will accept a string type as an argument to test for a match.
  • The method will return boolean true if there is a match using the regular expression and false if not.

See the above example live in JSBin.

If you want this as a utility function which you can reuse, here it is,

/* Check if string is valid date */
function checkIfValidDate(str) {
  // Regular expression to check if string is valid date
  const regexExp = /(?:(?:31(\/|-|\.)(?:0?[13578]|1[02]))\1|(?:(?:29|30)(\/|-|\.)(?:0?[13-9]|1[0-2])\2))(?:(?:1[6-9]|[2-9]\d)?\d{2})$|^(?:29(\/|-|\.)0?2\3(?:(?:(?:1[6-9]|[2-9]\d)?(?:0[48]|[2468][048]|[13579][26])|(?:(?:16|[2468][048]|[3579][26])00))))$|^(?:0?[1-9]|1\d|2[0-8])(\/|-|\.)(?:(?:0?[1-9])|(?:1[0-2]))\4(?:(?:1[6-9]|[2-9]\d)?\d{2})/gi;

  return regexExp.test(str);
}

// Use the function
checkIfValidDate("01-01-2021"); // true
checkIfValidDate("32-01-2021"); // false
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That's all! 😃

Feel free to share if you found this useful 😃.


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