3.rb

1.haml

-# Super cheapo minification!
-# Here's how it works:
-#
-# * The HAML below points to the minified version on production,
-#   or prints <script> tags if not.
-#
-# * We define the route to /js/script.js ourselves.
-#
-# * Some silly caching will ensure that the minification only happens once.

- if settings.production?
  %script{:type => 'text/javascript', :src => '/js/script.js?%s' % [settings.js_files.mtime.to_i] }

- else
  - settings.js_files.hrefs.each do |href|
    %script{:type => 'text/javascript', :src => href}

2.rb

path   = settings.root_path(%w(public js))
files  = Dir["#{path}/jquery.*.js"]
files += Dir["#{path}/lib.*.js"]
files += Dir["#{path}/admin.js"]
files += Dir["#{path}/admin.*.js"]

# Here's the magic.
Main.set :js_files, JsFiles.new(files)

class Main
  # This serves the minified JS.
  get '/js/script.js' do
    js = settings.admin_js
    content_type :js
    last_modified js.mtime
    etag js.mtime.to_i
    cache_control :public, :must_revalidate, :max_age => 86400

    js.compressed
  end
end

3.rb

# This class represents a list of JS files.
# Take note of how #compressed is implemented: it means that
# the files will always only be compressed once.

class JsFiles
  attr_accessor :files

  def initialize(files, options={})
    @files, @options = files, options
    @options[:prefix] ||= '/js/'
  end

  def mtime
    @mtime ||= @files.map { |f| File.mtime(f) }.max
  end

  def combined
    @combined ||= @files.map { |file| File.open(file) { |f| f.read } }.join("\n")
  end

  def compressed
    require 'jsmin'
    @compressed ||= JSMin.minify(combined).strip
  end

  def hrefs
    @files.map { |f| @options[:prefix] + File.basename(f) }
  end
end