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Sinatra AssetPack

Asset packer for Sinatra

This is the most convenient way to set up your CSS/JS (and images) in a Sinatra app. Seriously. No need for crappy routes to render Sass or whatever. No-siree!

  1. Drop your assets into /app like so (you can configure directories don't worry):
    • JavaScript/CoffeeScript files in /app/js
    • CSS/Sass/Less/CSS files in /app/css
    • Images into /app/images
  2. Add register Sinatra::AssetPack and set up options to your app (see below)
  3. Use <%= css :application %> to your layouts. Use this instead of messy script and link tags
  4. BOOM! You're in business baby!


Sinatra AssetPack is a simple Ruby gem. You can install it via gem install.

$ gem install sinatra-assetpack

Bundler users

If you use Bundler, you will need to add it to your Gemfile.

gem 'sinatra-assetpack', :require => 'sinatra/assetpack'


Install the plugin and add some options. (Feel free to omit the Optional items, they're listed here for posterity):

require 'sinatra/assetpack'

class App < Sinatra::Base
  set :root, File.dirname(__FILE__)
  register Sinatra::AssetPack

  assets {
    serve '/js',     from: 'app/js'        # Optional
    serve '/css',    from: 'app/css'       # Optional
    serve '/images', from: 'app/images'    # Optional

    # The second parameter defines where the compressed version will be served.
    # (Note: that parameter is optional, AssetPack will figure it out.)
    js :app, '/js/app.js', [

    css :application, '/css/application.css', [

    js_compression  :jsmin      # Optional
    css_compression :sass       # Optional

Using in layouts

In your layouts, use the css and js helpers: (Use haml? Great! Use != css :youreawesome instead.)

<%= css :application, :media => 'screen' %>
<%= js  :app %>

And then what?

Development mode

If you're on development mode, it serves each of the files as so:

<link rel='stylesheet' href='/css/screen.849289.css' media='screen' type='text/css' />
<script type='text/javascript' src='/js/vendor/jquery.283479.js'></script>
<script type='text/javascript' src='/js/vendor/underscore.589491.js'></script>
<script type='text/javascript' src='/js/app/main.589491.js'></script>

Production mode

If you're on production mode, it serves a compressed version in the URLs you specify:

<link rel='stylesheet' href='/css/application.849289.css' media='screen' type='text/css' />
<script type='text/javascript' src='/js/app.589491.js'></script>


  • CoffeeScript support Just add your coffee files in one of the paths served (in the example, app/js/ and they will be available as JS files (http://localhost:4567/js/hello.js).

  • Sass/Less/SCSS support Works the same way. Place your dynamic CSS files in there (say, app/css/screen.sass) and they will be available as CSS files (http://localhost:4567/css/screen.css).

  • Cache busting the css and js helpers automatically ensures the URL is based on when the file was last modified. The URL /js/jquery.js may be translated to /js/jquery.8237898.js to ensure visitors always get the latest version.

  • Images support Image filenames in your CSS will automatically get a cache-busting suffix (eg, /images/icon.742958.png).

  • Embedded images support You can embed images in your CSS files as data: URIs by simply adding ?embed to the end of your URL.

  • No intermediate files needed You don't need to generate compiled files. You can, but it's optional. Keeps your source repo clean!

  • Auto minification (with caching) JS and CSS files will be compressed as needed.

  • Heroku support Oh yes. That's right.


By default, AssetPack uses JSMin for JS compression, and simple regexes for CSS compression. You can specify other compressors in the assets block:

assets {
  js_compression  :jsmin    # :jsmin | :yui | :closure | :uglify
  css_compression :simple   # :simple | :sass | :yui | :sqwish

YUI Compressor

This uses Yahoo's Java-powered YUI compressor. For YUI compression, you need the YUI compressor gem (gem install yui-compressor).

assets {
  js_compression  :yui
  js_compression  :yui, :munge => true   # Munge variable names

  css_compression :yui

Note: This depends on the yui-compressor gem. You will need to install it. (gem install yui-compressor) If you use Bundler, you will need to add it to your Gemfile as well.

# Gemfile
gem 'yui-compressor', :require => 'yui/compressor'

SASS compression

For SASS compression, you need the Sass gem (gem install sass). This treats the CSS files as Scss files and uses Sass's :output => :compressed.

assets {
  css_compression :sass

Note: This depends on the sass gem. You will need to install it (gem install sass). If you use Bundler, you will need to add it to your Gemfile as well.

# Gemfile
gem 'sass'

Sqwish CSS compression

Sqwish is a NodeJS-based CSS compressor. To use Sqwish with AssetPack, install it using npm install -g sqwish. You need NodeJS and NPM installed.

assets {
  css_compression :sqwish
  css_compression :sqwish, :strict => true

Google Closure compression

This uses the Google closure compiler service to compress your JavaScript. Available levels are:

assets {
  js_compression :closure
  js_compression :closure, :level => "SIMPLE_OPTIMIZATIONS"

UglifyJS compression

This uses the UglifyJS compressor to compress your JavaScript. You will need to install the uglifier gem.

For options, refer to the Uglifier documentation.

assets {
  js_compression :uglify
  js_compression :uglify, [options]

Note: This depends on the uglifier gem. In your Gemfile, you will need to add it. For Heroku support, you will need to add the therubyracer-heroku gem as well.

# Gemfile
gem 'uglifier'

# If you're on Heroku:
gem "therubyracer-heroku", "0.8.1.pre3", :require => false


To show images, use the img helper. This automatically adds width, height, and a cache buster thingie. ImageMagick is required to generate full image tags with width and height.

<!-- Original: --> <%= img '/images/email.png' %>
<!-- Output:   --> <img src='/images/email.873842.png' width='16' height='16' />

URL translation

In your CSS files, url()'s will automatically be translated.

/* Original: */    .email { background: url(/images/email.png); }
/* Output:   */    .email { background: url(/images/email.6783478.png); }

Image embedding

Want to embed images as data: URI's? Sure! Just add ?embed at the end of the URL.

/* Original: */    .email { background: url(/images/email.png?embed); }
/* Output:   */    .email { background: url(data:image/png;base64,NF8dG3I...); } 

Need to build the files?

Actually, you don't need to—this is optional! But add this to your Rakefile:

# Rakefile
APP_FILE  = 'app.rb'

require 'sinatra/assetpack/rake'


Now invoke the assetpack:build Rake task. This will create files in /public.

$ rake assetpack:build

API reference

Assets block

All configuration happens in the assets block. You may invoke it in 2 ways:

class App < Sinatra::Base
  register Sinatra::AssetPack

  # Style 1
  assets do
    css :hello, [ '/css/*.css' ]
    js_compression :yui

  # Style 2
  assets do |a|
    a.css :hello, ['/css/*.css' ]
    a.js_compression :yui

Getting options

Invoking it without a block allows you to access the options. This works for almost all the options, with the exception for css, js and serve.

App.assets.js_compression   #=> :yui


Serves files from LOCALPATH in the URI path PATH. Both parameters are required.

# Usage
serve 'PATH', :from => 'LOCALPATH'


This makes /app/javascripts/vendor/jquery.js available as http://localhost:4567/js/vendor/jquery.js.

serve '/js', from: '/app/javascripts'


Sets the compression engine to use for JavaScript or CSS. This defaults to :jsmin and :simple, respectively.

If OPTIONS_HASH is given as a hash, it sets options for the engine to use.

# Usage:
assets {
  js_compression :ENGINE
  js_compression :ENGINE, OPTIONS_HASH
  css_compression :ENGINE
  css_compression :ENGINE, OPTIONS_HASH


Yo seriously check this out: the first line uses Sqwish with it's defaults, and the second line uses Sqwish with it's magic.

assets {
  css_compression :sqwish
  css_compression :sqwish, :strict => true


Sets the options for the compression engine to use. This is usually not needed as you can already set options using js_compression and css_compression.

# Usage:
assets {
  js_compression_options HASH
  css_compression_options HASH


This sets the option for :munge for the CSS compression engine.

css_compression_options :munge => true


Adds packages to be used.

The NAME is a symbol defines the ID for that given package that you can use for the helpers. That is, If a CSS package was defined as css :main, [ ... ], then you will need to use <%= css :main %> to render it in views.

the URI is a string that defines where the compressed version will be served. It is optional. If not provided, it will default to "/assets/name.type" (eg: /assets/main.css).

the PATHs is an array that defines files that will be served. Take note that this is an array of URI paths, not local paths.

If a PATH contains wildcards, it will be expanded in alphabetical order. Redundancies will be taken care of.

# Usage:
assets {
  css :NAME, [ PATH1, PATH2, ... ]
  css :NAME, 'URI', [ PATH1, PATH2, ... ]
  js:NAME, [ PATH1, PATH2, ... ]
  js:NAME, 'URI', [ PATH1, PATH2, ... ]


In this example, JavaScript files will be served compressed as /js/application.js (default since no URI is given). The files will be taken from ./app/javascripts/vendor/jquery*.js.

class App < Sinatra::Base
  assets {
    serve '/js', from: '/app/javascripts'
    js :application, [

# In views: <%= js :application %>


Excludes any URL paths that match the given spec.

These files will not show up in packages, and they will not be accessible.

By default, .* and _* are ignored. The former protects folders such as .svn from being accessed, and the latter protects Sass partial files from being accessed directly.

Note that this matches against URL paths, not local file paths. This means something like *.scss will not work, as all stylesheet files will be compiled to .css.

# Usage:
assets {
  ignore FILESPEC


Here's an example.

class App < Sinatra::Base
  assets {
    # Ignores all files matching *.private.js in any folder.
    ignore '*.private.js'

    # Ignores all files in `/app/js/foo/**/*`
    ignore '/js/foo'

Advanced usage

By default, .* and _* are ignored. To disable this behavior, you can use clear_ignores! before your ignore lines.

assets {
  ignore '*.private.js'

To check if a certain file is ignored, use assets.ignore?

assets.ignored?("/css/_chrome.css")   #=> true


Caches the built packages on application startup.

If this is not used, the packages will be minified when they are first requested. This only has an effect in the production environment (or when Sinatra's reload_templates is otherwise set to false).

# Usage:
prebuild {true|false}


In this example, the package for :application will be built when the application is started in the production environment.

class App < Sinatra::Base
  assets {
    js_compression :closure

    js :application, [
    prebuild true

# $ RACK_ENV=production ruby app.rb
# ** Building /assets/application.js...
# == Sinatra/1.2.6 has taken the stage on 4567 for production
# >> Thin web server (v1.2.11 codename Bat-Shit Crazy)
# >> Maximum connections set to 1024
# >> Listening on, CTRL+C to stop

API reference: helpers

These are helpers you can use in your views.

<%= css %>

Shows a CSS package named PACKAGE. If OPTIONS_HASH is given, they will we passed onto the <link> tag to be generated as attributes.

You may specify as many packages as you need, as shown in the second usage line.

# Usage:
<%= css :PACKAGE %>

Example 1

This links to the main stylesheet for screen media.

<%= css :main, media: 'screen' %>

<!-- Output: -->
<link rel='stylesheet' type='text/css' href='/css/main.873984.css' media='screen' />

Example 2

You may also invoke it with multiple packages.

<%= css :base, :app, :main, media: 'screen' %>

<!-- Output: -->
<link rel='stylesheet' type='text/css' href='/css/base.873984.css' media='screen' />
<link rel='stylesheet' type='text/css' href='/css/app.873984.css' media='screen' />
<link rel='stylesheet' type='text/css' href='/css/main.873984.css' media='screen' />

<%= js %>

Same as css, but obviously for JavaScript. You may also specify as many packages as you need, just with css.

# Usage:
<%= js :PACKAGE %>


This example embeds the main package with an ID.

<%= js :main, id: 'main_script' %>

<!-- Output: -->
<script type='text/javascript' src='/js/main.783439.js' id='main_script'></script>

<%= img %>

Shows an <img> tag from the given SRC. If the images is found in the asset directories (and ImageMagick is available), width and height attributes will be added.

# Usage:
img 'SRC'

If OPTIONS_HASH is given, they will we passed onto the <img> tag to be generated as attributes.


This example renders an image with an alt tag.

<%= img '/images/icon.png', alt: 'Icon' %>

<!-- Output: -->
<img src='/images/icon.834782.png' width='24' height='24' alt='Icon' />`

Need Compass support?

No, AssetPack doesn't have built-in Compass support, but you can use Sinatra Support.

For an example of how to use AssetPack with Compass, including on how to use it to generate image sprites, see the Compass example application.

# gem install sinatra/support
Encoding.default_external = 'utf-8'
require 'sinatra/support'

class Main
  register Sinatra::CompassSupport


© 2011, Rico Sta. Cruz. Released under the MIT License.

Sinatra-AssetPack is authored and maintained by Rico Sta. Cruz with help from it's contributors. It is sponsored by my startup, Sinefunc, Inc.

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