Regular Expressions 101

(?<=\D|^)(?<year>\d{4})(?<sep>[^\w\s])(?<month>1[0-2]|0[1-9])\k<sep>(?<day>0[1-9]|[12][0-9]|(?<=11\k<sep>|[^1][4-9]\k<sep>)30|(?<=1[02]\k<sep>|[^1][13578]\k<sep>)3[01])(?=\D|$)

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Description

A fully tested regex that extracts and validates date parts using named capturing groups.

Validations:

Year must be preceded by nothing or a non-digit character
Year must have 4 digits
Month must be between 01 and 12
Month must have 2 digits
Day must be between 01 and the maximum number of days for the month (e.g. february can't have more than 29 days)
Day must have 2 digits
Day must be followed by nothing or a non-digit character
Separator must be any single character that is not a space or an alphanumeric character
Separator must be the same between each date part

Capturing groups:

| # |   Name  | Description                         |
|:-:|:-------:|-------------------------------------|
| 1 |  `year` | 4 digits of the year                |
| 2 |  `sep`  | Date parts separator                |
| 3 | `month` | 2 digits of the month               |
| 4 |  `day`  | 2 digits of the date (day of month) |

Example usage:

let match = regex.exec('2020-11-22')

console.log('year: %s, month: %s, day: %s',
            match.groups.year,
            match.groups.month,
            match.groups.day)

// year: 2020, month: 11, day: 22

Compatibility: (updated 2020-11-20)

Chrome >= 64
Edge >= 79
Firefox >= 78
IE incompatible (lookbehind assertions & named capture groups not supported)
Opera >= 51
Safari incompatible (lookbehind assertions not supported)
NodeJS >= 10.0.0

See regex compatibility table.

Note: does not validate leap years (not really possible in regex)

Submitted by Elie Grenon (DrunkenPoney) <elie.grenon.1@gmail.com>

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