timezone-js

TimezoneJS.Date

A timezone-enabled, drop-in replacement for the stock JavaScript Date. The timezoneJS.Date object is API-compatible with JS Date, with the same getter and setter methods -- it should work fine in any code that works with normal JavaScript Dates.

Mailing list

Overview

The timezoneJS.Date object gives you full-blown timezone support, independent from the timezone set on the end-user's machine running the browser. It uses the Olson zoneinfo files for its timezone data.

The constructor function and setter methods use proxy JavaScript Date objects behind the scenes, so you can use strings like '10/22/2006' with the constructor. You also get the same sensible wraparound behavior with numeric parameters (like setting a value of 14 for the month wraps around to the next March).

The other significant difference from the built-in JavaScript Date is that timezoneJS.Date also has named properties that store the values of year, month, date, etc., so it can be directly serialized to JSON and used for data transfer.

Setup

First you'll need to include the code on your page. Both timezoneJS.Date, and the supporting code it needs in timezoneJS.timezone are bundled in the date.js file in src directory. Include the code on your page with a normal JavaScript script include, like so:

<script type="text/javascript" src="/js/timezone-js/src/date.js">

Next you'll need the Olson time zone files -- timezoneJS.Date uses the raw Olson data to calculate timezone offsets. The Olson region files are simple, structured text data, which download quickly and parse easily. (They also compress to a very small size.)

Then you'll need to make the files available to the timezoneJS.timezone code, and initialize the code to parse your default region. (This will be North America if you don't change it). No sense in downloading and parsing timezone data for the entire world if you're not going to be using it.

Put your directory of Olson files somewhere under your Web server root, and point timezoneJS.timezone.zoneFileBasePath to it. Then call the init function. Your code will look something like this:

timezoneJS.timezone.zoneFileBasePath = '/tz';
timezoneJS.timezone.init();

If you use timezoneJS.Date with Fleegix.js, there's nothing else you need to do -- timezones for North America will be loaded and parsed on initial page load, and others will be downloaded and parsed on-the-fly, as needed. If you want to use this code with some other JavaScript toolkit, you'll need to define your own transport method in the loadZoneFile method.

Usage

Create a timezoneJS.Date the same way as a normal JavaScript Date, but append a timezone parameter on the end:

var dt = new timezoneJS.Date('10/31/2008', 'America/New_York');
var dt = new timezoneJS.Date(2008, 9, 31, 11, 45, 'America/Los_Angeles');

Naturally enough, the getTimezoneOffset method returns the timezone offset in minutes based on the timezone you set for the date.

// Pre-DST-leap
var dt = new timezoneJS.Date(2006, 9, 29, 1, 59, 'America/Los_Angeles');
dt.getTimezoneOffset(); => 420
// Post-DST-leap
var dt = new timezoneJS.Date(2006, 9, 29, 2, 0, 'America/Los_Angeles');
dt.getTimezoneOffset(); => 480

Just as you'd expect, the getTime method gives you the UTC timestamp for the given date:

var dtA = new timezoneJS.Date(2007, 9, 31, 10, 30, 'America/Los_Angeles');
var dtB = new timezoneJS.Date(2007, 9, 31, 12, 30, 'America/Chicago');
// Same timestamp
dtA.getTime(); => 1193855400000
dtB.getTime(); => 1193855400000

You can set (or reset) the timezone using the setTimezone method:

var dt = new timezoneJS.Date('10/31/2006', 'America/Juneau');
dt.getTimezoneOffset(); => 540
dt.setTimezone('America/Chicago');
dt.getTimezoneOffset(); => 300
dt.setTimezone('Pacific/Honolulu');
dt.getTimezoneOffset(); => 600

The getTimezone method tells you what timezone a timezoneJS.Date is set to.

var dt = new timezoneJS.Date('12/27/2010', 'Asia/Tokyo');
dt.getTimezone(); => 'Asia/Tokyo'

Customizing

If you don't change it, the timezone region that loads on initialization is North America (the Olson 'northamerica' file). To change that to another reqion, set timezoneJS.timezone.defaultZoneFile to your desired region, like so:

timezoneJS.timezone.zoneFileBasePath = '/tz';
timezoneJS.timezone.defaultZoneFile = 'asia';
timezoneJS.timezone.init();

If you want to preload multiple regions, set it to an array, like this:

timezoneJS.timezone.zoneFileBasePath = '/tz';
timezoneJS.timezone.defaultZoneFile = ['asia', 'backward', 'northamerica', 'southamerica'];
timezoneJS.timezone.init();

By default the timezoneJS.Date timezone code lazy-loads the timezone data files, pulling them down and parsing them only as needed.

For example, if you go with the out-of-the-box setup, you'll have all the North American timezones pre-loaded -- but if you were to add a date with a timezone of 'Asia/Seoul,' it would grab the 'asia' Olson file and parse it before calculating the timezone offset for that date.

You can change this behavior by changing the value of timezoneJS.timezone.loadingScheme. The three possible values are:

1. timezoneJS.timezone.loadingSchemes.PRELOAD_ALL -- this will preload all the timezone data files for all reqions up front. This setting would only make sense if you know your users will be using timezones from all around the world, and you prefer taking the up-front load time to the small on-the-fly lag from lazy loading.
2. timezoneJS.timezone.loadingSchemes.LAZY_LOAD -- the default. Loads some amount of data up front, then lazy-loads any other needed timezone data as needed.
3. timezoneJS.timezone.loadingSchemes.MANUAL_LOAD -- Preloads no data, and does no lazy loading. Use this setting if you're loading pre-parsed JSON timezone data.

Pre-Parsed JSON Data

If you know beforehand what specific cities your users are going to be using, you can reduce load times specifically by creating a pre-parsed JSON data file containing only the timezone info for those specific cities.

The src directory contains a command-line JavaScript script that can generate this kind of JSON data. Note that this script requires the Rhino (Java) JavaScript engine to run, since the stock SpiderMonkey (C) engine doesn't come with file I/O capabilities.

Use the script like this:

rhino preparse.js zoneFileDirectory [exemplarCities] > outputfile.json

The first parameter is the directory where the script can find the Olson zoneinfo files. The second (optional) param should be a comma-delimited list of timzeone cities to create the JSON data for. If that parameter isn't passed, the script will generate the JSON data for all the files.

rhino preparse.js olson_files \
"Asia/Tokyo, America/New_York, Europe/London" \
> major_cities.json

rhino preparse.js olson_files > all_cities.json

Once you have your file of JSON data, set your loading scheme to timezoneJS.timezone.loadingSchemes.MANUAL_LOAD, and load the JSON data with loadZoneJSONData, like this:

var _tz = timezoneJS.timezone;
_tz.loadingScheme = _tz.loadingSchemes.MANUAL_LOAD;
_tz.loadZoneJSONData('/major_cities.json', true);

Since the limited set of data will be much smaller than any of the zoneinfo files, and the JSON data is deserialized with eval, this method is significantly faster than the default setup. However, it only works if you know beforehand exactly what timezones you want to use.

Compressing

The Olson timezone data files are simple, space- and linefeed-delimited data. The abundance of whitespace means they compress very, very well.

If you plan to use timezoneJS.Date in a production Web app, it's highly recommended that you first strip the copious comments found in every Olson file, and serve compressed versions of the files to all browsers that can handle it. (Note that IE6 reports itself as able to work with gzipped data, but has numerous problems with it.)

Just to give you an idea of the difference -- merely stripping out the comments from the 'northamerica' file reduces its size by two-thirds -- from 103K to 32K. Gzipping the stripped file reduces it down to 6.5K -- probably smaller than most of the graphics in your app.

The src directory has a sample Ruby script that you can use to strip comments from Olson data files.

Development

Feel free to fork and modify at your own will. The source code is annotated and doc can be generated with docco

Testing

This library requires timezone info from IANA database. Download the data and put timezone files into lib/tz

It also uses jasmine-node as the testing framework. In order to run the tests, do npm test

Feel free to add more tests.