text: function extend(Child, Parent) {
      Child.prototype = Object.create(Parent.prototype);
      Child.prototype.constructor = Child;
  };
  
  function Shape() {
  
  };
  
  Shape.prototype.duplicate = function () {
      console.log('duplicate');
  };
  
  function Circle() {
  
  };
  
  extend(Circle, Shape);
  
  // must be after extend(Circle, Shape);
  Circle.prototype.duplicate = function () {
      // pulling from the parents prototype
      Shape.prototype.duplicate.call(this)
      // adding to the current prototype
      console.log('duplicate circle');
  };
  
  const c = new Circle();