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Simple, transparent CoffeeScript support for Rails and Rack apps.
Ruby CoffeeScript
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Barista is a set of tools to make using CoffeeScript in Rails 3, Rails 2 and Rack applications easier. You can think of it as similar to Compass, but for CoffeeScript instead of Sass.

As an added bonus, Barista also gives:

  • Automatic support for a :coffeescript filter in Haml (when Haml is loaded before Barista) — automatically converting inline CoffeeScript to JavaScript for you.
  • Where possible, support for coffeescript_include_tag and coffeescript_tag.
  • When possible, instead of pre-compiling in development and test modes, Barista will embed CoffeeScript in the page for you.
  • Support for Heroku via therubyracer-heroku and either pre-compiled JS or, optionally, a lightweight Rack app that generates on request.

Getting Started

Out of the box, Barista has semi-automatic support for Rails 3.0, Rails 2 (currently untested) and Sinatra. With a minimal amount of effort, you can also make it work in any Rack-based framework.

Rails 3

Adding Barista to your Rails 3 application should as simple as adding two gems to your Gemfile, and running two commands. To get started, open up your Gemfile and add the following:

gem "json" # Only needed if on Ruby 1.8 / a platform that ships without JSON
gem "barista"

Next, you'll need to run the the following:

bundle install
rails g barista:install

This will install the gem into your application and will generate a file in config/initializers/barista_config.rb that contains a set of options to configure Barista options.

Place your CoffeeScripts in app/coffeescripts and Barista will automatically compile them on change into public/javascripts.

Rails 2

Much like on Rails 3, Barista supports deep integration into Rails 2. The only thing missing (that is currently supported in the Rails 3 version) is built in support for generating a config file. If you're using bundler in your application, all you need to do is add:

gem "json" # Only needed if on Ruby 1.8 / a platform that ships without JSON
gem "barista"

To your Gemfile. If you're not using bundler, doing gem install json barista and requiring barista both in your application should be enough to get you started.

If you wish to change the barista configuration, take a look at the Rails 3 initializer and modify it to suite your application as needed.

If you wish to use barista tasks with rails 2 project, add

load "barista/tasks/barista.rake"

To your Rakefile.


Adding Barista to a Sinatra application is a relatively straight forward affair. Like in Rails 2 and Rails 3, you first need to add and require the barista gem and (optionally, the json gem). Unlike Rails 2 and 3 (which set it up automatically), you must also register the extension in your application. So, in the scope of your app (either the top level scope or the Sinatra::Application subclass you're using), you then need to simple add:

register Barista::Integration::Sinatra

Which will automatically set up the Barista environment and other similar details (e.g. the automatic compilation filter). Since you don't have initializers like you do in Rails, you can then simply run your Barista.configure call and block anywhere before your application starts serving requests.

Other Rack-based Frameworks

Lastly, even though it is built out of the box to support Rails and Sinatra, Barista can also be used with any Rack-based framework. For proper integration, several things must be done. Namely, wherever you declare your middleware (e.g. in a file), you should register the two pieces of middleware barista uses. Barista::Filter should only be registered when Barista performs compilation (e.g. in development mode) and Barista::Server::Proxy should be registered if you want it to support automatic serving of a coffeescript.js file and / or on the fly (versus pre-request compilation) of CoffeeScripts.

For example, your may look like:

# Setup goes here...
use Barista::Filter if Barista.add_filter?
use Barista::Server::Proxy
run MyRackApplication

Next, you need to configure barista anywhere before your the above code is run. e.g by adding the following immediatly preceeding it:

# Barista (for CoffeeScript Support)
Barista.app_root = root
Barista.root     = File.join(root, 'coffeescripts')
barista_config = root + '/barista_config.rb'
require barista_config if File.exist?(barista_config)

Hence, if you'e using, for example, serve users should have a that looks similar to this example.

A Quick Note on the JSON Gem

Barista indirectly requires the json gem via the coffee-script gem, but it isn't listed as a dependency for very good reasons. If you encounter errors relating to require 'json', Then you'll need to add either gem 'json' or gem 'json_pure' to your Gemfile.

If you're already running Ruby 1.9, this will be unnecessary as JSON is shipped as part of the standard library.

General Information

Barista transparently compiles CoffeeScript to JavaScript. When a .coffee file is changed and the page is refreshed, Barista first regenerates all .js files whose .coffee sources have been recently changed. This way, you can refresh immediately after saving the .coffee file and not worry about an old .js file being sent to the browser (as often happens when using coffee --watch).

Barista supports using therubyracer when installed or, by default, using either the node executable or jsc (on OS X) to compile your scripts. There is no need for you to install the coffee-script executable in Node as having Node itself, or any of the alternatives available, is enough.

When you want to deploy, you can simple run rake barista:brew to force the compilation of all JavaScripts for the current application.

In Practice

Barista not only supports compiling all JavaScripts on demand (via rake barista:brew as above, or Barista.compile_all!) but it also ships with a simple Rack server app that will compile on demand for platforms such as Heroku, meaning you don't need write access (although it is helpful).

If you're using Jammit, the precompilation phase (e.g. rake barista:brew before running Jammit) will make it possible for your application to automatically bundle not only normal JavaScripts but also your CoffeeScripts.

To add Barista to your project, simply add gem 'barista', '~> 1.0' to your Gemfile and run bundle install.

Please note that for Jammit compatibility, in test and development mode (by default) it will automatically compile all CoffeeScripts that have changed before rendering the page.

Barista works out of the box with Rails 3 (and theoretically, Rails 2) — with support for Rack if you're willing to set it up manually. More docs on how to set it up for other platforms will be posted in the near future.


To use Barista with Sinatra, you'll need to first require the Barista gem in your application and then add the following to your application scope (e.g. if you're using a custom class, there):

register Barista::Integration::Sinatra

This will automatically setup the filter as needed, setup a server proxy for the coffee-script.js file and setup the defaults based on your applications environment


Please note that Barista lets you configure several options. To do this, it's as simple as setting up an initializer with:

rails generate barista:install

Then editing config/initializers/barista_config.rb. The options available are:

Boolean Options

All of these come in the form of #option? (to check its status), #option=(value) (to set it) and #option! (to set the value to true):

  • verbose – Output debugging error messages. (Defaults to true in test / dev)
  • bare – Don't wrap the compiled JS in a Closure.
  • add_filter – Automatically add an around filter for processing changes. (Defaults to true in test / dev)
  • add_preamble – Add a time + path preamble to compiled JS. (Defaults to true in test / dev)
  • exception_on_error – Raise an exception on compilation errors (defaults to true)
  • embedded_interpreter – Embeds coffeescript + link to coffee file instead of compiling for include tags and haml filters. (Defaults to true in test / dev)
  • auto_compile – Automatically compile CoffeeScript to JS when CoffeeScript is newer than the generated JS file. After you turn it off, your server will use the generated JS file directly and won't depend on any CoffeeScript compilers. (Defaults is true)

Path options

  • root – The folder path to read CoffeeScripts from. (Defaults to app/coffeescripts.)
  • output_root – The folder to write compiled JS files to. (Defaults to public/javascripts.)
  • change_output_prefix! – Method to change the output prefix for a framework.
  • change_output_root! - Method to change the output root for a given framework.
  • verbose – Whether or not Barista will add a preamble to files.
  • js_path – Path to the pure-JavaScript compiler.
  • env – The application environment. (Defaults to Rails.env.)
  • app_root – The application's root path.
  • bin_path – The path to the node executable if non-standard and not using therubyracer.
  • All of the hook methods mentioned below.

Custom Preamble

You can generate a custom preamble using a code block. For example, you can replace the location of the original .coffee file by a relative one to Rails.root.

Barista.add_preamble do |location|
    "/* : DO NOT MODIFY - compiled from #{}\n\n"


One of the other main features Barista adds (over other tools) is frameworks similar to Compass. The idea being, you add CoffeeScripts at runtime from gems etc. To do this, in your gem just have a coffeescript directory and then in your gem add the following code:

Barista::Framework.register 'name', 'full-path-to-directory' if defined?(Barista::Framework)

For an example of this in practice, check out bhm-google-maps or, the currently-in-development, shuriken. The biggest advantage of this is you can then manage JS dependencies using existing tools like Bundler.

In your Barista.configure block, you can also configure on a per-application basis the output directory for individual frameworks (e.g. put shuriken into vendor/shuriken, bhm-google-maps into vendor/bhm-google-maps):

Barista.configure do |c|
  c.change_output_prefix! 'shuriken',        'vendor/shuriken'
  c.change_output_prefix! 'bhm-google-maps', 'vendor/bhm-google-maps'

Alternatively, to prefix all, you can use Barista.each_framework (if you pass true, it includes the 'default' framework which is your application root).

Barista.configure do |c|
  c.each_framework do |framework|
    c.change_output_prefix!, "vendor/#{}"


Barista lets you hook into the compilation at several stages, namely:

  • before compilation
  • after compilation
  • after compilation fails
  • after compilation complete

To hook into these hooks, you can do the following:

  • Barista.before_compilation { |path| puts "Barista: Compiling #{path}" }
  • Barista.on_compilation { |path| puts "Barista: Successfully compiled #{path}" }
  • Barista.on_compilation_with_warning { |path, output| puts "Barista: Compilation of #{path} had a warning:\n#{output}" }
  • Barista.on_compilation_error { |path, output| puts "Barista: Compilation of #{path} failed with:\n#{output}" }
  • Barista.on_compilation_complete { puts "Barista: Successfully compiled all files" }

These allow you to do things such as notify on compilation, automatically perform compression post compilation and a variety of other cool things.

An excellent example of these hooks in use is barista_growl, by Trevor Burnham — a gem perfect for development purposes that automatically shows Growl messages on compilation.

Contributors / Credits

The following people have all contributed to Barista:

Barista was originally heavily inspired by Bistro Car, but has taken a few fundamentally different approach in a few areas.

Barista builds upon the awesome coffee-script gem.

It's all possible thanks to CoffeeScript by Jeremy Ashkenas.

If I've missed you're name and you've contributed to Barista, please let me know and I'll add you to the list (or fork this document and send a pull request).

Note on Patches/Pull Requests

  1. Fork the project.
  2. Make your feature addition or bug fix.
  3. Add tests for it. This is important so I don't break it in a future version unintentionally.
  4. Commit, do not mess with rakefile, version, or history. (if you want to have your own version, that is fine but bump version in a commit by itself I can ignore when I pull)
  5. Send me a pull request. Bonus points for topic branches.


Copyright (c) 2010 Darcy Laycock. See LICENSE for details.

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