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srawlins / timezone

Time zone database and time zone aware DateTime object for Dart.
BSD 2-Clause "Simplified" License
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TimeZone

This package provides the IANA time zone database and time zone aware DateTime class, TZDateTime.

The current time zone database version is 2024a. See the announcement for details.

You can update to the current IANA time zone database by running tool/refresh.sh.

Initialization

TimeZone objects require time zone data, so the first step is to load one of our time zone databases.

We provide three different APIs to load a database: one which is embedded into a Dart library, one for browsers, and one for standalone environments.

Database variants

We offer three different variants of the IANA database:

Initialization from Dart library

This is the recommended way to initialize a time zone database for non-browser environments. Each Dart library found in lib/data, for example lib/data/latest.dart, contains a single no-argument function, initializeTimeZones.

import 'package:timezone/data/latest.dart' as tz;
void main() {
  tz.initializeTimeZones();
}

To initialize the all database variant, import 'package:timezone/data/latest_all.dart'. To initialize the 10y database variant, import 'package:timezone/data/latest_10y.dart'.

Initialization for browser environment

Import package:timezone/browser.dart library and run async function Future initializeTimeZone([String path]).

import 'package:timezone/browser.dart' as tz;

Future<void> setup() async {
  await tz.initializeTimeZone();
  var detroit = tz.getLocation('America/Detroit');
  var now = tz.TZDateTime.now(detroit);
}

To initialize the all database variant, call initializeTimeZone('packages/timezone/data/latest_all.tzf'). To initialize the 10y database variant, call initializeTimeZone('packages/timezone/data/latest_10y.tzf').

Initialization for standalone environment

Import package:timezone/standalone.dart library and run async function Future initializeTimeZone([String path]).

import 'package:timezone/standalone.dart' as tz;

Future<void> setup() async {
  await tz.initializeTimeZone();
  var detroit = tz.getLocation('America/Detroit');
  var now = tz.TZDateTime.now(detroit);
}

Note: This method likely will not work in a Flutter environment.

To initialize the all database variant, call initializeTimeZone('data/latest_all.tzf'). To initialize the 10y database variant, call initializeTimeZone('data/latest_10y.tzf').

Local Location

By default, when library is initialized, local location will be UTC.

To overwrite local location you can use setLocalLocation(Location location) function.

Future<void> setup() async {
  await tz.initializeTimeZone();
  var detroit = tz.getLocation('America/Detroit');
  tz.setLocalLocation(detroit);
}

API

Library Namespace

The public interfaces expose several top-level functions. It is recommended then to import the libraries with a prefix (the prefix tz is common), or to import specific members via a show clause.

Location

Each location in the database represents a national region where all clocks keeping local time have agreed since 1970. Locations are identified by continent or ocean and then by the name of the location, which is typically the largest city within the region. For example, America/New_York represents most of the US eastern time zone; America/Phoenix represents most of Arizona, which uses mountain time without daylight saving time (DST); America/Detroit represents most of Michigan, which uses eastern time but with different DST rules in 1975; and other entries represent smaller regions like Starke County, Indiana, which switched from central to eastern time in 1991 and switched back in 2006.

The tz database

Get location by tz database/Olson name

final detroit = tz.getLocation('America/Detroit');

See Wikipedia list for more database entry names.

We don't provide any functions to get locations by time zone abbreviations because of the ambiguities.

Alphabetic time zone abbreviations should not be used as unique identifiers for UTC offsets as they are ambiguous in practice. For example, "EST" denotes 5 hours behind UTC in English-speaking North America, but it denotes 10 or 11 hours ahead of UTC in Australia; and French-speaking North Americans prefer "HNE" to "EST".

The tz database

TimeZone

TimeZone objects represents time zone and contains offset, DST flag, and name in the abbreviated form.

var timeInUtc = DateTime.utc(1995, 1, 1);
var timeZone = detroit.timeZone(timeInUtc.millisecondsSinceEpoch);

TimeZone aware DateTime

The TZDateTime class implements the DateTime interface from dart:core, and contains information about location and time zone.

var date = tz.TZDateTime(detroit, 2014, 11, 17);

Converting DateTimes between time zones

To convert between time zones, just create a new TZDateTime object using from constructor and pass Location and DateTime to the constructor.

var localTime = tz.DateTime(2010, 1, 1);
var detroitTime = tz.TZDateTime.from(localTime, detroit);

This constructor supports any objects that implement DateTime interface, so you can pass a native DateTime object or our TZDateTime.

Listing known time zones

After initializing the time zone database, the timeZoneDatabase top-level member contains all of the known time zones. Examples:

import 'package:timezone/timezone.dart' as tz;
import 'package:timezone/data/latest.dart' as tz;

void main() {
  tz.initializeTimeZones();
  var locations = tz.timeZoneDatabase.locations;
  print(locations.length); // => 429
  print(locations.keys.first); // => "Africa/Abidjan"
  print(locations.keys.last); // => "US/Pacific"
}

Time Zone databases

We are using IANA Time Zone Database to build our databases.

We currently build three different database variants:

Updating Time Zone databases

Script for updating Time Zone database, it will automatically download the IANA time zone database and compile into our native format.

$ chmod +x tool/refresh.sh
$ tool/refresh.sh

Note, on Windows, you may need to follow these steps which use WSL.