padrino_assets.rb

module Padrino
  module Assets 
    def self.registered(app)
      app.set :assets_config, YAML.load_file(File.join(Padrino.root, 'config', 'assets.yml'))
      app.set :assets_path, File.join('app', 'client')
      # You must set this:
      # app.set :assets_base_url, ''

      ['require.config.js', 'app/', 'components/', 'dist/'].each do |path|
        route = path =~ /\/$/ ? "#{path}/*file" : path 
        app.get "/#{route}" do
          if params.include? :file
            file = File.join(Padrino.root, self.settings.assets_path, path, params[:file])
          else
            file = File.join(Padrino.root, self.settings.assets_path, path)
          end

          expires 0, :no_cache
          send_file file, :type => File.extname(file)
        end
      end

      app.helpers Padrino::Assets::Helpers
    end

    module Helpers
      ##
      # Returns an html script tag for each of the sources provided.
      # You can pass in the filename without extension or a symbol and we search it in your +appname.public_folder+
      # like app/public/javascript for inclusion. You can provide also a full path.
      #
      # @overload javascript_include_tag(*sources, options={})
      #   @param [Array<String>] sources   Splat of js source paths
      #   @param [Hash]          options   The html options for the script tag
      #
      # @return [String] Script tag for +sources+ with specified +options+.
      #
      # @example
      #   javascript_include_tag 'application', :extjs
      #
      # @api public
      def fingerprinted_javascript_include_tag(*sources)
        options = sources.extract_options!.symbolize_keys
        options.reverse_merge!(:type => 'text/javascript')
        sources.flatten.map { |source|
          content_tag(:script, nil, options.reverse_merge(:src => "#{self.settings.assets_base_url}#{fingerprinted_asset_path(source)}"))
        }.join("\n")
      end

      ##
      # Returns an html script tag for each of the sources provided.
      # You can pass in the filename without extension or a symbol and we search it in your +appname.public_folder+
      # like app/public/stylesheets for inclusion. You can provide also a full path.
      #
      # @overload stylesheet_link_tag(*sources, options={})
      #   @param [Array<String>] sources   Splat of css source paths
      #   @param [Hash]          options   The html options for the link tag
      #
      # @return [String] Stylesheet link html tag for +sources+ with specified +options+.
      #
      # @example
      #   stylesheet_link_tag 'style', 'application', 'layout'
      #
      # @api public
      def fingerprinted_stylesheet_link_tag(*sources)
        options = sources.extract_options!.symbolize_keys
        options.reverse_merge!(:media => 'screen', :rel => 'stylesheet', :type => 'text/css')
        sources.flatten.map { |source|
          tag(:link, options.reverse_merge(:href => "#{self.settings.assets_base_url}#{fingerprinted_asset_path(source)}"))
        }.join("\n")
      end

      private
      def fingerprinted_asset_path(source)
        fingerprinted = JSON.parse(File.open(File.join(Padrino.root, self.settings.assets_path, 'fingerprinted.json')).read)['files']
        fingerprinted[source]
      end
    end
  end # BBB
end # Padrino

Grunfile.js https://gist.github.com/2e3060fdf63f77937f7e. All the client code lies in app/client/.