file.rb

class SomePage
  
  def save
    save_button.click
    sleep 0.1 while loading?
  end
  
  def loading?
    loading_div.exists?
  end
  
  private
  
  def loading_div
    browser.div(:id, 'loading')
  end
  
  def save_button
    browser.button(:id, 'save')
  end
  
end

page = SomePage.new
page.fill_with data
page.save