app/controllers/cms/viewables_controller.rb
def update
      unique_key = UniqueKey.find(params[:id])

      if unique_key.update(unique_key_params)
        flash_now!(:success)
      else
        flash_now!(error: unique_key.errors.full_messages.first)
      end

      respond_to do |format|
        format.js {}
      end
    end
def update
      unique_key = UniqueKey.find(params[:id])

      if unique_key.update(unique_key_params)
        flash_now!(:success)
      else
        flash_now!(error: unique_key.errors.full_messages.first)
      end

      respond_to do |format|
        format.js {}
      end
    end
used by [data-js-cms-sortable] element to modify the viewable position within the list