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: http://groups.google.com/group/timezone-js

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:

   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.timzeone 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.

