Using Opal with Roda and Sprockets

Add Opal-Sprockets and Roda-Sprockets to your Gemfile (or install using gem):

# Gemfile
gem "opal-sprockets"
gem "roda-sprockets"
gem "puma"

Roda-Sprockets uses sprockets as its default build system, so the asset-pipeline from rails can be mimicked here to map all ruby assets in the /assets path to be compiled using opal.

Basic Application

require 'roda'

class App < Roda
   plugin :sprockets, precompile: %w(application.js),
                      prefix: %w(app/),
                      opal: true,
                      debug: ENV['RACK_ENV'] != 'production'
   plugin :public

   route do |r|

     r.root do
         <!doctype html>
             #{ javascript_tag 'application' }
             #{ opal_require 'application' }


This creates a sprockets instance under the /assets path, serving Opal assets from app/ with all the custom opal paths added automatically.

This env object includes all the opal corelib and stdlib paths. To add any custom application directories, you must add them to the load path using Opal.append_path or adding them to the prefix parameter. You can now add an app/application.rb file into this added path with some basic content:

# app/application.rb
require 'opal'

puts "wow, running ruby!"

It is necessary to require the opal corelib (seen in the require call) above. This just makes the Opal runtime and corelib available. Then it is possible to use all the corelib methods and classes, e.g. Kernel#puts as seen above.

Running Application

As this is just a simple Roda application, you can run it:

$ bundle exec rackup

And point your browser towards http://localhost:9292/ and view the browser debug console. You should see this message printed.

Extending the integration

It's possible to extend this integration, for that please look into the roda-sprockets documentation