Object-Specific Classes in Ruby and JavaScript (via non-standard __proto__)

object-specific_classes.js

rectangle = {
  width: 10,
  height: 8
}

rectangle.__proto__ = {
  area: function() {
    return this.width * this.height
  }
}

rectangle.area() // 80
Object.keys(rectangle) // ['width', 'height']

object-specific_classes.rb

rectangle = {
  :width => 10,
  :height => 8
}

class << rectangle
  def area
    self[:width] * self[:height]
  end
end

rectangle.area # 80
rectangle.keys # [:width, :height]