Check if Javascript is Enabled (Serverside) with Rails

How would you check if javascript is enabled in Rails? So that I could do something like this in the views:

<div>
    <% if javascript_enabled? %>
    <p>Javascript Enabled!</p>
    <%- else -%>
    <p>No Javascript</p>
    <%- end -%>
</div>

You can detect it, but it isn't pretty.

First, you need a new controller with an action that updates a timeout in the session:

class JavascriptController < ApplicationController
  def confirm
    session[:javascript_updated] = Time.now
  end
end

Next you need to include a javascript action in all your pages so this controller action is called on each page load. The easiest way is to include it on a "javascript-confirm.js" file included in your layout (on this particular example I used Prototype's Ajax.Request, so you need to have it included on your javascripts, too):

function confirmJavascript()
{
    // Assuming you are using Prototype
    new Ajax.Request('/JavascriptController/confirm');
}

myTimeoutFunction();
setInterval(myTimeoutFunction, 10000); // invoke each 10 seconds

This will invoke the confirm action in all your page views. Finally, you have to control how much time did it pass since your last confirmation in your application controller.

class ApplicationController < ActionController::Base

JAVASCRIPT_TIME_LIMIT = 10.seconds

before_filter :prepare_javascript_test

private
def prepare_javascript_test
  if (session[:javascript_updated].blank? or
     Time.now - session[:javascript_updated] > ApplicationController::JAVASCRIPT_TIME_LIMIT)
    @javascript_active = true
  else
    @javascript_active = false
  end
end

end

You will now have a variable called @javascript_active in all your controllers.

It should work even when the user activates/deactivates javascript, with a precision of 10 seconds. It might not work if some of your pages take longer than 10 pages to load (i.e. with lots of images). Increase the time limit in that case (on applicationcontroller and your javascript)

Disclaimer: I haven't tested this code, some bugs might be lurking - but it should point you on the right direction.