gistfile1.rb

  # The problem below is that the JS responses were not being cached properly
  # but the HTML responses were fine.

  caches_action :show, :layout => false, :expires_in => 24.hours

  def show
    respond_to do |wants|
      wants.html
      wants.js {
        # What... the... fuck... After tracing why the JS responses to this action
        # were not being action cached through rails' internals, this is what I
        # determined needed to be done.  For whatever reason, content_for_layout
        # in ActionController::Caching::Actions expects response.layout and
        # @cached_content_for_layout to be set when :layout => false is set.
        # They were set just fine for HTML responses but JS responses did not
        # have them set?!?!  Manually setting them here allows the JS responses to
        # get cached...
        response.layout = 'layouts/application' # Why?
        cached_content = render :partial => 'category_item'
        response.template.instance_variable_set('@cached_content_for_layout', cached_content) # WTF?
      }
    end
  end