subclassing.js

// Base class
function Shape (x, y) {

  this.x = x;
  
  this.y = y;

}


// Rectangle extends Shape
function Rectangle (x, y, width, height) {
  Shape.call(this, x, y);
  
  this.width = width;
  
  this.height = height;

}
Rectangle.prototype = Object.create(Shape.prototype);
Rectangle.prototype.constructor = Rectangle;