jstz.js GEMified for the Rails >= 3.1 asset pipeline
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Latest commit 3c5d573 Nov 5, 2013 6 @nbfritz nbfritz Update Rails version



This is jstz.js aka jsTimezoneDetect GEMified for the Rails >= 3.1 asset pipeline through the following:

bundle gem jstz-rails
cd jstz-rails
mkdir -p vendor/assets/javascripts
curl https://bitbucket.org/pellepim/jstimezonedetect/raw/c7ea46531444b600246fe651bc9feb66a7593be5/jstz.js -o vendor/assets/javascripts/jstz.js
echo "" >> README.md; echo "# jstz.js appended README #" >> README.md; echo "" >> README.md
curl https://bitbucket.org/pellepim/jstimezonedetect/raw/c7ea46531444b600246fe651bc9feb66a7593be5/README.md >> README.md
echo "" >> LICENSE; echo "# jstz.js appended LICENSE #" >> LICENSE; echo "" >> LICENSE
curl https://bitbucket.org/pellepim/jstimezonedetect/raw/c7ea46531444b600246fe651bc9feb66a7593be5/LICENCE.txt >> LICENSE
git add .
git commit -am "initial jstz-rails"
git remote add origin git@github.com:vanetten/jstz-rails.git
  • modify lib/jstz-rails/version.rb to match jstz.js version

      VERSION = ""
  • modify lib/jstz-rails.rb to subclass Rails::Engine

      class Engine < ::Rails::Engine
  • modify jstz-rails.gemspec

      gem.description   = "This gem provides jstz.js and for your Rails 3 application."
      gem.summary       = "Use jstz with Rails 3"
      gem.homepage      = "http://rubygems.org/gems/jstz-rails"
      gem.files = Dir["{lib,vendor}/**/*"] + ["LICENSE", "README.md"]
      gem.add_dependency "railties", "~> 3.1"
  • build

      rake build
  • release

      rake release


Add this line to your application's Gemfile:

gem 'jstz-rails'

And then execute:

$ bundle

Or install it yourself as:

$ gem install jstz-rails


Add to application.js

//= require jstz.js

Add to your.js to write browser detected timezone to a cookie

document.cookie = 'time_zone='+jstz.determine().timezone.name()+';';

Add to application_controller.rb to set application's timezone from cookie

before_filter :set_timezone
	def set_timezone
		Time.zone = cookies["time_zone"]

Or add to view to set default from cookie (e.g. simple_form)

<%= f.input :time_zone, priority: /US/, :default => ActiveSupport::TimeZone.all.reject {|zone| zone.tzinfo != TZInfo::Timezone.get(cookies["time_zone"])}.first.name %>


  1. Fork it
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Added some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create new Pull Request

jstz.js appended README


This script gives you the zone info key representing your device's time zone setting.

The return value is an IANA zone info key (aka the Olson time zone database).

The IANA timezone database is pretty much standard for most platforms (UNIX and Mac support it natively, and every programming language in the world either has native support or well maintained libraries that support it).

Example Use

There is a minified version in the repo called jstz.min.js. Include it in your HTML document.

Invoke the script by calling

    var tz = jstz.determine(); // Determines the time zone of the browser client
    tz.name(); // Returns the name of the time zone eg "Europe/Berlin"

Use Case

The script is useful if you do not want to disturb your users with questions about what time zone they are in. You can rely on this script to give you a key that is usable for server side datetime normalisations across time zones.


This script does not do geo-location, nor does it care very much about historical time zones.

So if you are unhappy with the time zone "Europe/Berlin" when the user is in fact in "Europe/Stockholm" - this script is not for you. (They are both identical in modern time).

Also, if it is important to you to know that in Europe/Simferopool (Ukraine) the UTC offset before 1924 was +2.67, sorry, this script will not help you.

Time zones are a screwed up thing, generally speaking, and the scope of this script is to solve problems concerning modern time zones, in this case from 2010 and forward.


There is an updated demo running on: http://pellepim.bitbucket.org/jstz/.


If you want to contribute to the project (perhaps fix a bug, or reflect a change in time zone rules), please simply issue a Pull Request. Don't worry about Grunt builds etc, all you need to modify is the jstz.js file and I'll take care of the testing/minifying etc.


Thanks to

Other contributors: Gilmore Davidson