prototype-rails provides Prototype, Scriptaculous, and RJS on Rails 3.1
and later.

Prototype and Scriptaculous are pulled in by the asset pipeline, so you don't
need to copy the source files into your app. You may reference them in your
s app/assets/javascripts/application.js:

    //= require prototype
    //= require prototype_ujs
    //= require effects
    //= require dragdrop
    //= require controls

prototype-rails supports RJS debugging. RJS responses are wrapped to catch
exceptions, alert() them, and re-raise the exception. Debugging is disabled by
default. To enable in development, set `config.action_view.debug_rjs = true`
in config/environments/development.rb.