Deploys shared JavaScript projects onto the CDN
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Helium is a Ruby application for running a Git-backed JavaScript package distribution system. It comes with a web frontend that allows Git-hosted projects to be downloaded, built and served from a single domain, allowing any number of other sites to use the projects and receive automatic updates when new versions are deployed.

Helium is free software, released under the GPL licence. Please see the LICENCE file for details.


The deployer is designed to allow JavaScript packages to be easily shared between client websites without the need to copy-paste code from project to project. It allows you to run a centralized server on which JavaScript code is deployed from Git repositories, letting you easily push code updates to any sites using the hosted scripts. Client sites are able to specify which branch or tag of a package they wish to use, and code dependencies are transparently handled so that each site loads only the code it needs.

The system is based around the JS.Class package manager (, which provides a pure-JavaScript dependency manager for on-demand loading of JavaScript objects. Helium programmatically generates a package listing from metadata stored in Git repositories, so that client projects using this system do not have to maintain the list themselves. The only code required in each client project is this:

<!-- Step 1. Load JS.Class package manager and the package listing -->
<script src="" type="text/javascript"></script>

<!-- Step 2. Declare which branches to use -->
<script type="text/javascript">
Helium.use('yui', '2.7.0');
Helium.use('ojay', '0.4.1');

After this, the require() function can be used to load any object deployed to the central server on demand. See the above-linked JS.Class documentation for more info.


Before deploying this app, you will need Ruby, RubyGems, Passenger (mod_rack), and Git installed on your webserver. Helium's web frontend assumes you will be using Rack to serve the application.

If you've checked Helium out from Git, use Bundler to install its dependencies:

gem install bundler
bundle install


To install from RubyGems:

gem install helium

To install from GitHub:

git clone git://
cd helium
gem build helium.gemspec
gem install helium-0.2.0.gem

With the gem installed, you can install a copy of the web app anywhere on your system using the he install command with the name of the directory to create:

he install helium-app

This will give you the following files:


The files deploy.yml and custom.js are editable through the web frontend, and must be writable by the web server. You can restrict write access to certain IP addresses using the configure block in, by default this is:

Helium::Web.configure do |config|
  config.allow_ips ['', '']

Apache setup

To serve this application, just set up an Apache VHost whose DocumentRoot is the helium-app/public directory. Passenger should do the rest.

In addition, the Apache user will need read/write access to helium-app/deploy.yml and helium-app/custom.js, which are editable through the web frontend. The application will generate a directory at helium-app/lib, which will be used to check out and build projects from Git, and will copy any generated JavaScript files to helium-app/public/js; Apache will need read/write access to these directories.


For the rest of this article, we'll assume the deployment app is running at, and the app is stored in the directory helium-app as described above.

JavaScript project setup

To deploy a project using this system, two conditions must be fulfilled: the project must be hosted in a Git repository, and it must have a jake.yml build file in its root directory. We use Jake ( to build checked-out projects and extract dependency data. Even if your project doesn't need a complex build process, it must still declare the objects it provides and requires so it can be deployed using the package manager. Each package must provide provides and (optionally) requires fields in its metadata. For example, here's a jake.yml file for a Panel package, which provides the panel function and Panel and PanelOverlay classes, and depends on JS.Class, Ojay, Ojay.HTML and Ojay.ContentOverlay:

source_directory:   .
build_directory:    .
layout:             together

    shrink_vars:    true
    private:        true


      - panel
        - panel
        - Panel
        - PanelOverlay
        - JS.Class
        - Ojay
        - Ojay.HTML
        - Ojay.ContentOverlay

The project must have a build called min, and may have other builds. This deployment system exports the min build for public use. You may use whatever compression settings you like for this build, and the project may contain any number of packages. See Jake ( for more documentation on these build files.

Note that objects listed under provides and requires should be the runtime reference names of JavaScript objects, and anything in the requires list should be provided by some other package known to the deploy system.

If you're starting a new project, Helium comes with a command line tool that generates some stub code, a jake.yml file and a test suite. Just run the following to create a new project, replacing project-name with the name of your library.

he create project-name

After generating a project, you will need to edit its dependencies in jake.yml and edit test/browser.html to reference your Helium server so that dependencies can be loaded.

Running jake from the new project directory will build the library for you and generate a JS.Packages manifest for it. The test page uses require() to load your library, so you'll know if any of its dependency data is missing.

Helium also comes with a command line tool for starting a webserver in a local directory; this is useful for testing code that requires a domain name, such as Ajax calls, Google Maps widgets, etc. Run this command to serve your test files using this server:

he serve project-name/test

The server runs on localhost:8000, so for example the file test/index.html will be available at http://localhost:8000/index.html on your machine.

The deployment process

Our deployment system performs the following steps on every project registered:

  • Copies its Git repo into helium-app/lib/repos/{project name}. If the repo is already present, we use git fetch to update it, otherwise we use git clone.

  • Exports the head revision of every branch and every tag in the repo into its own directory at helium-app/lib/static/{project}/{branch}.

  • Builds every exported copy using Jake, if a jake.yml is present. This stage extracts the provides and requires data from the Jake build process, keeping track of which build file provides which JavaScript objects.

  • Generates a file at helium-app/public/js/helium.js, which lists all the files that Jake has built and which objects they provide using the JS.Class package manager API (see

Using the deployment app

On first accessing, there will be no JavaScript projects listed. To add projects, we need to edit a YAML file listing projects and their Git URIs. To support the client-side package manager, the deploy system must at least have the JS.Class project registered. Projects are listed as key-value pairs by project name and Git URI.

Go to and enter the following projects:

  repository:       git://
  version:          3.0.1

  yui:              git://
  ojay:             git://

After clicking 'Save', these projects should be listed in the sidebar. Check all three, and hit 'Deploy' to import them all into the deploy system. After a few seconds you should see a log output telling you which projects and branches were built. There should also now be a JavaScript file at that lists the files available on the server.

Client-side package management

The client side of the distribution system is the JS.Class package manager (documented at This provides a dependency manager and a simple way to load JavaScript objects on demand. To set it up, you just need the following in the head of your HTML pages:

<script src="" type="text/javascript"></script>

<script type="text/javascript">
Helium.use('yui', '2.7.0');
Helium.use('ojay', '0.4.1');

To explain the above code: the file helium.js contains the JS.Class core and package manager and a list of packages generated by Helium during the build process. Then we need to configure the package manager; Helium.use() must be called to tell it which projects and which branch of each project we want to use. You can also set the variable Helium.PATH if you've set Helium up to serve script files from a nonstandard location. By default it is set to:

Helium.PATH = 'http://{ your domain }/js';

Note that the above only loads one external script – the Helium.use() calls do not load any extra code, they just tell the system which version of each project to use if and when we need to load them.

Loading libraries in JavaScript

With the above script tags in place, you should use the require function to declare which objects you want to use in each inline script. For example:

<script type="text/javascript">
require('Ojay.HTML', 'PanelOverlay', function() {

    var overlay = new PanelOverlay({width: 300, height: 200}),
        title   = Ojay.HTML.h2('Hello, world!');


Only require() the objects you're directly using. The package manager should handle loading any other objects your code depends on; that's what all the provides and requires data was for in the configuration files mentioned above. The package manager only downloads extra scripts if any of the objects needed to run your code are not defined; no script is ever loaded more than once per page.