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Javascript/CSS bundling at the Rack level
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A Rack middleware for grouping Javascripts and stylesheets into one single file (styles are grouped by media type).


$ sudo gem install rack-bundle



use Rack::Bundle, :public_dir => "path/to/app/public/dir"
run app

Sinatra it's almost the same as above, except you don't need to explicitly call run as Sinatra will handle that:

use Rack::Bundle, :public_dir => Sinatra::Application.public

As for Rails, google around how to add Rack middlewares to the stack. I'm too lazy right now to look it up. But as a general pointer, I know it's in ROOT/config/environment.rb.

By default, this middleware will use the file system for storing bundles. For Heroku and a few other setups where the application doesn't have permission to write to certain directories, you can store and serve bundles directly from a database. Like so:

use Rack::Bundle, :public_dir => 'path/to/public' do |rack_bundle| =

DatabaseStore assumes an environment variable called DATABASE_URL exists, which is an URL that the adapter can use to connect to a database (See examples). You can alternatively supply that as parameter. For instance:

use Rack::Bundle, :public_dir => 'path/to/public' do |rack_bundle| = "sqlite://foo.sqlite3"

By default, Rack::Bundle will look for original assets in the directory specified by the public_dir option. If it can't find an asset there, it will also look in ./tmp. This might be useful in situations where you want to compile your CSS or JavaScript (maybe using SASS or CoffeeScript), but can't write these compiled files to the public_dir, since you might be using a read-only filesystem like Heroku.

A few assumptions

There's a few assumptions that this middleware makes in order to work. Note that all of those will change soon:

  • That external Javascripts (read: not hosted on the same web server as the app itself) come first in the DOM. This may or may not be an issue for you, but I've experienced a few. I'll add automatic reordering soon.
  • That you're linking Javascripts inside the tag. It won't break your app if you don't. But scripts that sit outside will be ignored.
  • That if you're using DatabaseStore, you have a ./tmp directory.

How does it work

It parses the response body using Nokogiri, finds every reference to external scripts/stylesheets, locates them in the file system, bundles them, saves the bundle in the application's public directory, and replaces the references in the response for one single reference to the bundle(s).


This project is currently at very early stages of development, which in my case means I haven't bothered making it do what it's supposed to do fast. It's quite possible however that your app will still perform a lot better with it as is, depending on how lazy you were when writing your layouts/templates. After the first release I'll be addressing performance almost exclusively.

Compared to...

rack-bundle is, as of now, a lot simpler (as in less features) than solutions such as Jammit. But it is plug-and-play: you load up the middleware with a few configuration parameters and you're set. No need to modify templates, no helpers, nothing. Oh also, it's framework agnostic, and that's priceless.


It's as free as sneezing. Just give me credit ( if you make some extraordinary out of this.

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