So you need to display some datetimes in your new ember.js/angular/backbone UI and the times must be displayed for a timezone which is different from the logged on user.

Let us say we have an Event class in our rails application with the following attributes:

1
2
3
4
5
6

create_table :events do |t|
  t.string :event_name, null: false
  t.text :description
  t.datetime :start_at, null: false
  t.string :time_zone, null: false, default: 'UTC'
end

Rails uses the timezone format: Eastern Time (US & Canada)

Javascript (and therefore the moment-timezone library) use the format: America/New_York

Rails can easily convert this for you and return the proper js format in your json:

1
2
3
4
5
6
7
8

class Event < ActiveRecord::Base
  # ...

  def time_zone_mapping
    # time_zone => Eastern Time (US & Canada)
    ActiveSupport::TimeZone::MAPPING[self.time_zone] # => America/New_York
  end
end

and with moment.js and moment-timezone

1
2

// where 'event' is the js representation of your rails model
moment(event.startAt).tz(event.timeZoneMapping).format('dddd, MMMM Do YYYY h:mm a z');

You will want to ensure that all json is being rendered with UTC as the configured timezone in rails, i.e. config.time_zone = 'UTC' in your application config and/or Time.zone = 'UTC' in your api controller.

See also

• Ruby on Rails: Timezones
• ActiveSupport::TimeZone