RJS - Ruby JavaScript - Very cool addition to Ruby on Rails to do Javascript in Ruby:

The hardcore API documentation

RJS element and collection proxies

Rails RJS templates

From A comp.lang.ruby thread about the new features in Rails 1.1:

Here goes a few sample rjs calls: 


  # First buy appears the cart, subsequent buys highlight it 
  page[:cart].visual_effect(@cart.size == 1 ? :appear : :highlight) 


  # Replace the cart with a refresh rendering of the cart partial 
  page[:cart].replace_html :partial => "cart" 


  # Highlight all the DOM elements of class "product" 
  page.select(".product").each do |element| 
    element.visual_effect :highlight 
  end 


  # Call the custom JavaScript class/method AddressBook.cancel() 
  page.address_book.cancel 


  # 4 seconds after rendering, set the font-style of all company 
  # spans inside tds to normal 
  page.delay(4) do 
    page.select("td span.company").each do |column| 
      column.set_style :fontStyle => "normal" 
    end 
  end