require 'singleton'

module Like
end

module Like::JavaScript
  class Undefined
    include Singleton
  
    def to_s
      'undefined'
    end
  
    # called by puts
    def to_ary
      ['undefined']
    end
  end
  
  # Ruby method is not a closure
  # undefined = Undefined.instance
  # would be of not much use
  class ::Object
    def undefined
      Undefined.instance
    end
  end
  
  class Object
    def method_missing(m)
      undefined
    end
  end

  class Array < ::Array
    def [](m)
      fetch(m, undefined)
    end
  end
end

# gem install minitest
require 'minitest/autorun'
  
module Like::JavaScript
  class UndefinedTest < Minitest::Test
    def test_variable
      assert_raises NameError do
        foo
      end
    end

    def test_to_s
      assert_equal 'undefined', undefined.to_s
    end

    def test_object_missing
      o = Object.new
      assert_equal undefined, o.foo
    end

    def test_array_missing
      a = Array.new
      assert_equal undefined, a[0]
    end

    def test_array_exists
      a = Array.new([:foo])
      assert_equal :foo, a[0]
    end
  end
end