Using Opal with Sinatra

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

# Gemfile
source 'https://rubygems.org'

gem 'sinatra'
gem 'opal-sprockets'
gem 'puma'

Opal-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

# config.ru
require 'opal-sprockets'
require 'sinatra'

opal = Opal::Sprockets::Server.new {|s|
  s.append_path 'app'
  s.main = 'application'
  s.debug = ENV['RACK_ENV'] != 'production'
}

map '/assets' do
  run opal.sprockets
end

get '/' do
  <<-HTML



        #{ Opal::Sprockets.javascript_include_tag('application', debug: opal.debug, sprockets: opal.sprockets, prefix: 'assets/' ) }


  HTML
end

run Sinatra::Application

This creates a simple sprockets instance under the /assets path. Opal
uses a set of load paths to compile assets using sprockets. The
Opal::Environment instance is a simple subclass of Sprockets::Environment
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
env.append_path. 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 sinatra 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.