Asset Pipeline

Dependency Management

Sprockets is a tool for managing libraries of JavaScript (and CoffeeScript) code, declaring dependency management and include 3rd-party code. At its core, Sprockets makes a require method available inside your .js and .coffee files which can pull in the contents of an external file from your project or from a 3rd party gem.

Say I have a file called jquery.js which contains the jQuery library and another file called app.js which contains my application code. My app file can include jquery before it runs like so:

//= require "jquery"

$(document).ready(function() {
    param1: true,
    param2: "maybe"

This system also works within CSS files:

 *= require base

body {
  font-weight: bold;

If you're using Sass you should stick with Sass' @import rule rather than using Sprockets directives.

Deploying combined assets only

If you prefer to deploy only the combined (concatenated) assets to the build directory with middleman build command, you should use the underscore-names for your ingredient assets. Example: the main /source/javascripts/all.js file is used for all dependencies:

//= require "_jquery"
//= require "_my_lib_code"
//= require "_my_other_code"

and the /source/javascripts/ directory should contain files: _jquery.js, _my_lib_code.js, _my_other_code.js. The resulting /build/javascripts/ directory will contain the all.js file only, with all dependant code included.

Asset Gems

You can use assets from gems by including them in your Gemfile, like this:

gem "bootstrap-sass", :require => false

The :require => false bit is important - many of these gems assume you're running in Rails, and break when they try to hook into Rails' or Compass' internals. Just avoid requiring the gems and Middleman will take care of the rest.

Once you've added a dependency on these gems, any images and fonts from the gem will be included in your project automatically. JavaScript and CSS are also available to be requireed or @imported into your own files.

If you want to refer to a gem stylesheet or JS file directly from your HTML rather than including it in your own assets, you'll need to import it explicitly in config.rb:

sprockets.import_asset 'jquery-mobile'

Then you can refer to that asset directly from script tags or javascript_include_tag.

Sprockets Import Path

If you have assets in directories other than your :js_dir or :css_dir, you can make them importable by adding them to your Sprockets import path.

Warning Make sure that you add a directory via #append_path only once, otherwise you will get duplicate entries in middleman's site map - one entry for each directory entry in the #appended_paths list. This might cause doubled building times, build conflicts if you minify your assets etc.

Add this to your config.rb:

# String
sprockets.append_path '/my/shared/assets1/'

# Pathname is also supported

If you have a list of directories and want to iterate over it, you can use this small code snippet to make sure every directory is only added once:

%w(path1 longer/path2 longer/path3).each do |path|
  next if sprockets.appended_paths.include? path

  sprockets.append_path path

Sprockets supports Bower, so you can add your Bower components path directly:

sprockets.append_path File.join root, 'bower_components'

To make your bower controlled assets - images, fonts etc. - available within your application, you need to import them using sprockets.import_asset. Given your component is called jquery, you can import all files mentioned in the main-section of the bower.json by using the following statement in your config.rb:

sprockets.import_asset 'jquery'

If you prefer to import a specific asset you need to use its relative path, which is <component_name>/<path_to_asset>:

sprockets.import_asset 'jquery/dist/jquery.js'

If you need to set an individual output path, you can pass #import_asset a block. This block gets the logical path of the asset as Pathname and needs to return the output path for the asset.

sprockets.import_asset('jquery/dist/jquery.js') do |logical_path|'javascripts_new.d') + logical_path
  # => javascripts_new.d/jquery/dist/jquery.js

Make sure to use parentheses for #import_asset if you are using curly braces for the block! Otherwise the block might get passed to another method and not to #import_asset and you wonder why the output path is not set correctly.

sprockets.import_asset('jquery/dist/jquery.js') { |logical_path|'javascripts_new.d') + logical_path }

To automate this a bit, you can use file lists from rake. Another option might be hike. You CANNOT use sprockets.each_file for this, because sprockets on top-level in config.rb is a faked sprocket environment and therefor this method is not available. But be careful, you might need to add gem "rake" or gem "hike" to your project-Gemfile to make this work.

require 'rake/file_list'
require 'pathname'

bower_directory = 'vendor/assets/components'

# Build search patterns
patterns = [
  '.png',  '.gif', '.jpg', '.jpeg', '.svg', # Images
  '.eot',  '.otf', '.svc', '.woff', '.ttf', # Fonts
  '.js',                                    # Javascript
].map { |e| File.join(bower_directory, "**", "*#{e}" ) }

# Create file list and exclude unwanted files*patterns) do |l|
  l.exclude { |f| !File.file? f }
end.each do |f|
  # Import relative paths


There are helpers available to be used within your *.scss files:

Those helpers prepend the correct directory/url to your asset, e.g. image_path('lightbox2/img/close.png') becomes images/lightbox2/img/close.png. To reference a bower controlled asset you need to use its relative name lightbox2/img/close.png for an image which is part of the lightbox2-component.


Middleman comes with Compass support out of the box. Compass is a powerful framework for writing cross-browser stylesheets in Sass. Compass also has its own extensions, like Susy, which you can use in Middleman. All of Sprockets' path helpers like image_url are hooked into the Middleman Sitemap, so other extensions (like :asset_hash) will affect your stylesheets too.