0_instructions.txt

Some brief instructions on how to use Sprocket 2 in Rails to get CoffeeScript
powered JS and SASS powered CSS with YUI compression all via the magic of rack.

This stuff will be native in Rails 3.1 and the layout of the files on the
filesystem will be different but this guide will get you working with it
while we wait for all that to finalize.

Ignore the number prefixes on each file. This is just to ensure proper order in the Gist.

It's based on eric1234 gist https://gist.github.com/911003. ijust made it 3.1 compliant in terms of convention

1_Gemfile.rb

gem 'coffee-script'
gem 'yui-compressor', :require => 'yui/compressor'
gem 'sass'
gem 'json' # sprocket dependency for Ruby 1.8 only
gem 'sprockets', :git => 'git://github.com/sstephenson/sprockets.git'

# Sprockets needs to build JS file. On mac it uses apple java compiler, on production server (linux for example) you need to 
# install this gem
group :production do
  gem "therubyracer"
end

2_asset_server.rb

# better than subclassing Sprockets::Environment according to Josh

Assets = Sprockets::Environment.new(Rails.root) do |env|
  assets =  ["javascripts", "stylesheets", "images", "fonts"]
  paths =   ["app/assets/", "lib/assets/", "vendor/assets/" ].map{|path| assets.map{|folder| "#{path}#{folder}" } }.flatten

  paths.each{ |path| env.append_path path }

  if Rails.env.staging? || Rails.env.production?
    env.js_compressor = YUI::JavaScriptCompressor.new :munge => true, :optimize => true
    env.css_compressor = YUI::CssCompressor.new
  end
end

3_routes.rb

# Mount the rack end-point for JavaScript and CSS.
MyApp::Application.routes.draw do
  # Add this line 
  mount Assets => '/assets'
end

4_application.js

# Put this in your app/assets/javascripts/application.js directory and call /assets/application.js in your browser
# You need to have jquery and jquery_ujs files (jquery_ujs is sometimes named rails.js)
#
# In your layout just add
#
#   <%= javascript_include_tag "/assets/application" %>
#
# In Rails 3.1 you could even do
#
#  <%= javascript_include_tag "application" %>
#
//= require jquery
//= require jquery_ujs
//= require_tree .

5_your_file.js.coffee

# Put this in your app/assets/javascripts directory, it will be included when you call /assets/application.js in your browser
alert 'hello world'

7_application.css

// Put this in your app/assets/stylesheets directory and call /assets/application.css in your browser
// In your layout just add
//
//   <%= stylesheet_link_tag "/assets/application" %>
//
// In Rails 3.1 you could even do
//
//  <%= stylesheet_link_tag "application" %>
//

/*
 *= require_tree . 
*/

7_your_file.css.scss

// Put this in your app/assets/stylesheets directory and call /assets/application.css in your browser
body {margin: 2px + 5px}

8_conclusion.txt

Sprockets 2 has a lot more under the hood but this gets you started.
A few things not covered:

1. Anything supported by Tilt can be used as a template engine
   (not just Sass and CoffeeScript).
2. Although Sass has native abilities to include other files, Sprockets 2
   gives the ability to all formats through special comments like:
     // =require "foo"
   It's special commands can be fairly powerful (like requiring an entire
   directory or tree). NOTE: Use the comment character relevant for the
   language. So coffescript should be:
     # =require 'foo.js'
   Then you can create 'foo.js.coffee' and when served it will be as one
   file.
3. Sprockets 2 has the ability to pre-compile the assets for maximum speed.
   Also useful when the deployment environment doesn't support a template
   language (like CoffeeScript).

@niuage have figured out how to use image path helpers?

Sorry, I upgraded to rails 3.1 a long time ago and I had not fixed the issue before that.