Opal Singleton method in Instance method

opal_singleton.rb

class App
  def init_obj
    @obj = Object.new

    @obj.define_singleton_method :foo do |arg|
      p 'singleton foo'
      return if arg == 1
      puts 'bar'
    end
  end

  def run_obj
    @obj.foo(0)
    @obj.foo(1)
  end
end

app = App.new

app.init_obj

app.run_obj