Overview

Run this code in your browser

class User
  attr_accessor :name

  def initialize(name)
    @name = name
  end

  def admin?
    @name == 'Admin'
  end
end

user = User.new('Bob')

# the output will go to your browser's console
puts user
puts user.admin?

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Getting Started: Rack and Sprockets

Add rack & opal-sprockets to your Gemfile.

gem 'rack'
gem 'opal-sprockets'

Setup the Opal rack-app in your config.ru as follows:

require 'opal-sprockets'

run Opal::Server.new { |server|
  # the name of the ruby file to load. To use more files they must be required from here (see app)
  server.main = 'application'
  # the directory where the code is (add to opal load path )
  server.append_path 'app'
}

Add a file named hello_world.js.rb to app/ with your hello world:

require 'opal'
require 'native'
$$.alert 'Hello World from Opal!'

Then start the server with bundle exec rackup and visit http://localhost:9292.

Learn more about Opal Sprockets

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Getting Started: Rails

Add opal-rails to your Gemfile or build your Rails app with Opal support: rails new -j opal

gem 'opal-rails'

Rename app/assets/javascripts/application.js to app/assets/javascripts/application.js.rb and replace its contents with this code:

require 'opal'
require 'opal_ujs'
require 'turbolinks'
require_tree '.'

Create a "Hello World" controller:

bin/rails generate controller HelloWorld index

Replace the contents of app/assets/javascripts/hello_world.js.rb with:

Document.ready? do
  Element.find('body').html = '<h1>Hello World from Opal!</h1>'
end

Start the server with bin/rails server and visit: http://localhost:3000/hello_world/index.

Learn more about Opal Rails

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Getting Started: Command Line Interface (CLI)

Install opal from Rubygems:

gem install opal

Write this code to hello_world.js.rb:

require 'ostruct'
greeting = OpenStruct.new(type: :Hello, target: :World, source: :Opal)
puts "#{greeting.type} #{greeting.target} from #{greeting.source}!"

Run it with Node.js (assuming it's installed):

opal hello_world.js.rb
# => Hello World from Opal!

Compile it to a JavaScript file:

opal -c hello_world.js.rb > hello_world.js
node hello_world.js
# => Hello World from Opal!

For a full list of supported options see:

opal --help

Learn more about the CLI

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Resources