# toIso8601String method

String toIso8601String ()

Returns an ISO-8601 full-precision extended format representation.

The format is `yyyy-MM-ddTHH:mm:ss.mmmuuuZ` for UTC time, and `yyyy-MM-ddTHH:mm:ss.mmmuuu` (no trailing "Z") for local/non-UTC time, where:

- `yyyy` is a, possibly negative, four digit representation of the year, if the year is in the range -9999 to 9999, otherwise it is a signed six digit representation of the year.
- `MM` is the month in the range 01 to 12,
- `dd` is the day of the month in the range 01 to 31,
- `HH` are hours in the range 00 to 23,
- `mm` are minutes in the range 00 to 59,
- `ss` are seconds in the range 00 to 59 (no leap seconds),
- `mmm` are milliseconds in the range 000 to 999, and
- `uuu` are microseconds in the range 001 to 999. If microsecond equals 0, then this part is omitted.

The resulting string can be parsed back using parse.

## Implementation

    String toIso8601String() {
      String y =
          (year >= -9999 && year <= 9999) ? _fourDigits(year) : _sixDigits(year);
      String m = _twoDigits(month);
      String d = _twoDigits(day);
      String h = _twoDigits(hour);
      String min = _twoDigits(minute);
      String sec = _twoDigits(second);
      String ms = _threeDigits(millisecond);
      String us = microsecond == 0 ? "" : _threeDigits(microsecond);
      if (isUtc) {
        return "$y-$m-${d}T$h:$min:$sec.$ms${us}Z";
      } else {
        return "$y-$m-${d}T$h:$min:$sec.$ms$us";
      }
    }