skip_trackable if javascript

gistfile1.txt

class CatalogController < ApplicationController
  prepend_before_action :skip_trackable, :only => [:index]
  before_filter :authenticate_user!, :except => [:show, :index]
    
  def skip_trackable
    request.env['devise.skip_trackable'] = true if request.env["HTTP_X_REQUESTED_WITH"] == "XMLHttpRequest"
  end


However I still see in my log:
 (0.3ms)  UPDATE `users` SET `last_activity_at` = '2013-08-28 02:48:26', `updated_at` = '2013-08-28 02:48:26' WHERE `users`.`id` = 1


based details on: http://stackoverflow.com/questions/17791626/devise-make-a-request-without-resetting-the-countdown-until-a-user-is-logged-o

because of:
unless warden.request.env['devise.skip_trackable']
  warden.session(scope)['last_request_at'] = Time.now.utc
end

I do not know if the before_filters occur before the warden call but it appears they don't which is why the post refers to prepend_before_action; which i've not researched well enough yet to know the difference.