Rails: Automatically set user timezone during signup

Sometimes you need to know the timezone of your users to perform some actions. For instance, you might want to send an email to your users every evening, at say 5pm. To make sure that the email goes out at 5pm in their timezone, you might want to find out what timezone they are in.

One way to do this is to use Rails’ time_zone_select tag and ask the user to save their time zone during sign up. However, we can skip this step by automatically reading the timezone information from the browser, and set it in a cookie. This cookie can then be accessed in our Rails controller and we can save the timezone in the User model.

Install jsTimezoneDetect

To read the timezone information correctly, let’s use the jsTimezoneDetect library. I’m not going into the details of how to add it to your Rails project, but I recommend using Bower to manage your frontend dependencies. For this tutorial, I suggest following the instructions to setup bower with your Rails app.

Make sure you have the library loaded correctly by opening the JS console in the browser and typing jstz.determine().name(). This should return your timezone.

Set the timezone in a cookie

We will set a cookie called timezone with the string we get from jsTimezoneDetect. The setCookie helper function sets the cookie with the value we pass in, and sets the expiry at 24 hours.

function setCookie(key, value) {
  var expires = new Date();
  expires.setTime(expires.getTime() + (24 * 60 * 60 * 1000));
  document.cookie = key + '=' + value + ';expires=' + expires.toUTCString();
}

jQuery(function() {
  var tz = jstz.determine().name();
  setCookie('timezone', tz);
})

We can now access the timezone from the server side using the cookie.

Updating the user

For this example, let’s assume you’re using Devise for user signup. We will override the default Devise RegistrationsController and add an after_action hook that saves the timezone to the User model.

The code below assumes that your users table contains a timezone field. Please create a migration to add the field if you don’t have it.

# config/routes.rb
devise_for :users, controllers: { registrations: 'registrations' }

# app/controllers/registrations_controller.rb
class RegistrationsController < Devise::RegistrationsController
  after_action :save_user_timezone, only: [:create]

  private

  def save_user_timezone
    return unless resource.persisted?
    resource.update(timezone: cookies[:timezone])
  end
end

Even though the above example is for Devise, we can easily modify the after_action hook for non-Devise registrations controllers too.

Next steps

You might want to make sure that you update the user whenever they login from a new timezone. We can achieve this by moving the after_action hook to the ApplicationController and update the timezone if it has changed.

However, in many cases you might only want to do this during sign up to give the user a sane default, and not want to change it unless the user explicitly wants to change it. In such cases, you will find the time_zone_select tag very useful in creating a form for updating the timezone.