• Opal is Ruby to JavaScript compiler
• Opal is written in Ruby
• Opal is dialect of Ruby itself
• Files writtein in Opal have extension .rb or .opal
• Files written in Opal are compiled server-side
• On the client-side pure JavaScript is executed

• JavaScript sucks big time
• No, seriously
• It was written in 10 days
• The author is homophobic (related?)
• "JavaScript - The good parts" has ~115 pages
• It is a fucking joke NaNNaNNaNNaNNaN
• People do not want to deal with it anymore

• Google started Dart
• Google has Java to JavaScript compiler
• JavaScript has been generated by many frameworks just that the developers do not need to touch it
• Coffeescript is popular
• Over 50 other languages that compile to JavaScript were developed 
  https://github.com/jashkenas/coffeescript/wiki/List-of-languages-that-compile-to-JS

 # Gemfile
 gem 'opal-rails'

 # app/assets/javascripts/application.js
 //= require opal
 //= require opal_ujs
 //= require_tree .

 # app/asset/javascripts/my_app.js.opal
 puts "Hello, good sirs!" # check the console!

 require 'opal-jquery'

 Document.ready? do
   Element.find('h1').html = 'Manipulating DOM like a sir!'
 end 

• In your template you include application.js
• Request goest to Sprockets
• Sprockets processes application.js and includes Opal-to-JavaScript DOM bindings
• Sprockets processes my_app.js.opal and compiles it's contents to JavaScript
• Pure JavaScript is served to the client

• Opal comes with DOM API built-in, classes as Document, Element are pre-defined
• Opal wraps standard JavaScript classes into more Ruby-esque API, i.e. Array implements Enumerable
• opal-jquery provides simple jQuery bindings
• It is possible to call other JavaScript in-line with something like `window.alert('foo');`

• a lot!
• classes, inheritance, modules
• instance/class variables, attr_accessor, super
• method_missing
• reflection - is_a? kind_of? etc.
• basic Ruby interfaces are implemented (i.e. Enumerable, Hash, Array, Proc)
• procs and lambdas
• self and method execution context is fixed
• blocks

class User
  attr_accessor :name

  def initialize(name)
    @name = name
  end

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

user = User.new('Bob')
m = user.method(:admin?)
puts m
puts m.call
puts m.is_a?(Array)

• Opal is best used with Rails
• Support for ERB and Haml on client-side (one-way bindings only)
• Some client-side MVC frameworks start to emerge (Vienna)
• Some client-and-frontend side frameworks start to appear (https://github.com/voltrb/volt)
• Bi-directional calls: Opal to JavaScript (``) and JavaScript to Opal (Opal.Foo.$new().$bar() etc.)
• RSpec implementation in browser
• It works!

• Thread and stuff
• File/IO
• rubygems
• DRB
• Major parts of Ruby STD lib

• cool
• useful already for small projects
• needs better client-side MVC framework
• would be much cooler if was compiled on client-side (like Amber Smalltalk)
• could be compiled to asm.js instead of JavaScript