A pattern, as described at http://joda-time.sourceforge.net/apidocs/org/joda/time/format/DateTimeFormat.html; if omitted will use ISO standard date formatting.
timeZone
String, default: null
The time zone (e.g. 'America/Los_Angeles'); defaults to UTC.
Examples
Code Editor (JavaScript)
// Various examples of ee.Date.format with Joda-Time formatting and time zones.
var date = ee.Date('2020-08-18'); // Defaults to UTC
print(date); // Date (2020-08-18 00:00:00)
// List of time zones:
// https://www.joda.org/joda-time/timezones.html
print(date.format(null, 'GMT')); // 2020-08-18T00:00:00
print(date.format(null, 'Etc/GMT')); // 2020-08-18T00:00:00
print(date.format(null, 'Etc/GMT+0')); // 2020-08-18T00:00:00
print(date.format(null, 'Zulu')); // 2020-08-18T00:00:00
print(date.format(null, 'UTC')); // 2020-08-18T00:00:00
print(date.format(null, 'America/Los_Angeles')); // 2020-08-17T17:00:00
print(date.format(null, 'US/Pacific')); // 2020-08-17T17:00:00
print(date.format(null, 'Etc/GMT+8')); // 2020-08-17T17:00:00
print(date.format(null, 'PST8PDT')); // 2020-08-17T17:00:00
print(date.format(null, 'Australia/Tasmania')); // 2020-08-18T10:00:00
print(date.format(null, 'Etc/GMT-10')); // 2020-08-18T10:00:00
// Reference for Joda-Time format characters:
// http://joda-time.sourceforge.net/apidocs/org/joda/time/format/DateTimeFormat.html
var datetime = ee.Date('1975-07-23T21:13:59'); // Defaults to UTC
print(datetime); // Date (1972-07-25 21:13:59)
// year of era and era
print(datetime.format('YYYY GG')); // 1975 AD
// century and year
print(datetime.format('CC YY')); // 19 75
// weekyear and week of weekyear
print(datetime.format('xxxx ww')); // 1975 30
// year and day of year
print(datetime.format('yy DDD')); // 75 204
// month of year and day of month
print(datetime.format('MM dd')); // 07 23
// day of week number and day of week text
print(datetime.format('e E')); // 3 Wed
print(datetime.format('e EEEEEEEE')); // 3 Wednesday
// half of day, hour of halfday, and clockhour of halfday
print(datetime.format('a K h')); // PM 9 9
print(datetime.format('a KK hh')); // PM 09 09
// hour of day, clockhour of day, minute, second, fraction of second
print(datetime.format('H k m s S')); // 21 21 13 59 0
print(datetime.format('HH kk mm ss SS')); // 21 21 13 59 00
// time zone
print(datetime.format('z')); // UTC
print(datetime.format('zzzz')); // Coordinated Universal Time
print(datetime.format('z', 'PST8PDT')); // PDT
print(datetime.format('zzzz', 'PST8PDT')); // Pacific Daylight Time
// time zone offset/id
print(datetime.format('Z')); // +0000
print(datetime.format('ZZ')); // +00:00
print(datetime.format('ZZZ')); // UTC
print(datetime.format('Z', 'PST8PDT')); // -0700
print(datetime.format('ZZ', 'PST8PDT')); // -07:00
print(datetime.format('ZZZ', 'PST8PDT')); // Pacific Daylight Time
// single quotes for text
print(datetime.format("YY 'yada' MM")); // 75 yada 07
// '' for a single quote
print(datetime.format("YY ''MM'' dd")); // 75 '07' 23