google ajax

asset_host.rb

google_paths = {
  'prototype' => 'http://ajax.googleapis.com/ajax/libs/prototype/1.6.0.2/',
  'controls'  => 'http://ajax.googleapis.com/ajax/libs/scriptaculous/1.8.1/',
  'dragdrop'  => 'http://ajax.googleapis.com/ajax/libs/scriptaculous/1.8.1/',
  'effects'   => 'http://ajax.googleapis.com/ajax/libs/scriptaculous/1.8.1/'
}

config.action_controller.asset_host = Proc.new do |source, request|
  google_asset = google_paths.keys.detect { |asset| source.starts_with?("/javascripts/#{asset}") }
  google_asset ? google_paths[google_asset] : "#{request.protocol}#{request.host_with_port}"
end

module.rb

module ActionView
  module Helpers
    module GoogleAssetTagHelper
      GOOGLE_PATHS = {
        'prototype' => 'http://ajax.googleapis.com/ajax/libs/prototype/1.6.0.2/prototype',
        'controls'  => 'http://ajax.googleapis.com/ajax/libs/scriptaculous/1.8.1/controls',
        'dragdrop'  => 'http://ajax.googleapis.com/ajax/libs/scriptaculous/1.8.1/dragdrop',
        'effects'   => 'http://ajax.googleapis.com/ajax/libs/scriptaculous/1.8.1/effects'
      }

      def self.included(base)
        base.send :alias_method_chain, :expand_javascript_sources, :google unless ActionController::Base.consider_all_requests_local
      end

      def expand_javascript_sources_with_google(sources)
        google_sources, normal_sources = sources.partition { |source| GOOGLE_PATHS.include? source }
        GOOGLE_PATHS.values_at(*google_sources) + expand_javascript_sources_without_google(normal_sources)
      end
    end
  end
end

ActionView::Base.class_eval do
  include ActionView::Helpers::GoogleAssetTagHelper
end