Repository: date-fns/date-fns
File: src/parseJSON/index.ts (TypeScript)

Code before:
 * This is a minimal implementation for converting dates retrieved from a JSON API to
 * a `Date` instance which can be used with other functions in the `date-fns` library.
 * The following formats are supported:
 *
 * - `2000-03-15T05:20:10.123Z`: The output of `.toISOString()` and `JSON.stringify(new Date())`
 * - `2000-03-15T05:20:10Z`: Without milliseconds
 * - `2000-03-15T05:20:10+00:00`: With a zero offset, the default JSON encoded format in some other languages
 * - `2000-03-15T05:20:10+05:45`: With a positive or negative offset, the default JSON encoded format in some other languages
 * - `2000-03-15T05:20:10+0000`: With a zero offset without a colon
 * - `2000-03-15T05:20:10`: Without a trailing 'Z' symbol
 * - `2000-03-15T05:20:10.1234567`: Up to 7 digits in milliseconds field. Only first 3 are taken into account since JS does not allow fractional milliseconds
 * - `2000-03-15 05:20:10`: With a space instead of a 'T' separator for APIs returning a SQL date without reformatting
 *
 * For convenience and ease of use these other input types are also supported
 * via [toDate]{@link https://date-fns.org/docs/toDate}:
 *
 * - A `Date` instance will be cloned
 * - A `number` will be treated as a timestamp
 *
 * Any other input type or invalid date strings will return an `Invalid Date`.
 *
 * @param {String|Number|Date} argument A fully formed ISO8601 date string to convert
 * @returns {Date} the parsed date in the local time zone
 * @throws {TypeError} 1 argument required
 */
export default function parseJSON(argument: Date | string | number): Date {
  requiredArgs(1, arguments)

  if (typeof argument === 'string') {
    const parts = argument.match(
      /(\d{4})-(\d{2})-(\d{2})[T ](\d{2}):(\d{2}):(\d{2})(?:\.(\d{0,7}))?(?:Z|(.)(\d{2}):?(\d{2})?)?/
    )
    if (parts) {
      // Group 8 matches the sign
      return new Date(
        Date.UTC(
          +parts[1],
          +parts[2] - 1,
          +parts[3],
          +parts[4] - (+parts[9] || 0) * (parts[8] == '-' ? -1 : 1),
          +parts[5] - (+parts[10] || 0) * (parts[8] == '-' ? -1 : 1),
          +parts[6],
          +((parts[7] || '0') + '00').substring(0, 3)
        )
      )
    }
    return new Date(NaN)
  }
  return toDate(argument)
}


Review comment (suggestion):
Let's make it `string`. I know that originally it was like that, but having this kind of type is demising the whole idea of types 😉

```suggestion
export default function parseJSON(argument: string): Date {
```

Code after:
 * This is a minimal implementation for converting dates retrieved from a JSON API to
 * a `Date` instance which can be used with other functions in the `date-fns` library.
 * The following formats are supported:
 *
 * - `2000-03-15T05:20:10.123Z`: The output of `.toISOString()` and `JSON.stringify(new Date())`
 * - `2000-03-15T05:20:10Z`: Without milliseconds
 * - `2000-03-15T05:20:10+00:00`: With a zero offset, the default JSON encoded format in some other languages
 * - `2000-03-15T05:20:10+05:45`: With a positive or negative offset, the default JSON encoded format in some other languages
 * - `2000-03-15T05:20:10+0000`: With a zero offset without a colon
 * - `2000-03-15T05:20:10`: Without a trailing 'Z' symbol
 * - `2000-03-15T05:20:10.1234567`: Up to 7 digits in milliseconds field. Only first 3 are taken into account since JS does not allow fractional milliseconds
 * - `2000-03-15 05:20:10`: With a space instead of a 'T' separator for APIs returning a SQL date without reformatting
 *
 * For convenience and ease of use these other input types are also supported
 * via [toDate]{@link https://date-fns.org/docs/toDate}:
 *
 * - A `Date` instance will be cloned
 * - A `number` will be treated as a timestamp
 *
 * Any other input type or invalid date strings will return an `Invalid Date`.
 *
 * @param {String|Number|Date} argument A fully formed ISO8601 date string to convert
 * @returns {Date} the parsed date in the local time zone
 * @throws {TypeError} 1 argument required
 */
export default function parseJSON(argument: string): Date {
  requiredArgs(1, arguments)

  if (typeof argument === 'string') {
    const parts = argument.match(
      /(\d{4})-(\d{2})-(\d{2})[T ](\d{2}):(\d{2}):(\d{2})(?:\.(\d{0,7}))?(?:Z|(.)(\d{2}):?(\d{2})?)?/
    )
    if (parts) {
      // Group 8 matches the sign
      return new Date(
        Date.UTC(
          +parts[1],
          +parts[2] - 1,
          +parts[3],
          +parts[4] - (+parts[9] || 0) * (parts[8] == '-' ? -1 : 1),
          +parts[5] - (+parts[10] || 0) * (parts[8] == '-' ? -1 : 1),
          +parts[6],
          +((parts[7] || '0') + '00').substring(0, 3)
        )
      )
    }
    return new Date(NaN)
  }
  return toDate(argument)
}