greeter.js

Greeter = Opal.class('Greeter', {
    'initialize': function(name) {
        this.set_first_name(name);
    },
    'greet': function() {
        this.puts('Hi, ' + this.first_name());
    },
    'first_name': function() {
        return this._first_name;
    },
    'set_first_name': function(name) {
        this._first_name = name;
    }
});

greeter.rb

class Greeter
  
  def initialize(name)
    self.first_name = name
  end
  
  def greet
    puts "Hi, #{first_name}"
  end
  
  attr_accessor :first_name
  
end