//Shape - superclass
function Shape() {
 this.x = 0;
 this.y = 0;
}

Shape.prototype.move = function(x, y) {
  this.x += x;
  this.y += y;
  console.info("Shape moved.");
};

// Rectangle - subclass
function Rectangle() {
 Shape.call(this); //call super constructor.
}

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

var rect = new Rectangle();

rect instanceof Rectangle //true.
rect instanceof Shape //true.

rect.move(1, 1); //Outputs, "Shape moved."

const util = require('util');
const EventEmitter = require('events');

function MyStream() {
  EventEmitter.call(this);
}

util.inherits(MyStream, EventEmitter);

MyStream.prototype.write = function(data) {
  this.emit('data', data);
}

var stream = new MyStream();

console.log(stream instanceof EventEmitter); // true
console.log(MyStream.super_ === EventEmitter); // true

stream.on('data', (data) => {
 console.log(`Received data: "${data}"`);
})
stream.write('It works!'); // Received data: "It works!"

exports.inherits = function(ctor, superCtor) {

 if (ctor === undefined || ctor === null)
  throw new TypeError('The constructor to "inherits" must not be ' +
            'null or undefined');

 if (superCtor === undefined || superCtor === null)
  throw new TypeError('The super constructor to "inherits" must not ' +
            'be null or undefined');

 if (superCtor.prototype === undefined)
  throw new TypeError('The super constructor to "inherits" must ' +
            'have a prototype');

 ctor.super_ = superCtor;
 Object.setPrototypeOf(ctor.prototype, superCtor.prototype);
};

Object.setPrototypeOf = Object.setPrototypeOf || function (obj, proto) {
 obj.__proto__ = proto;
 return obj; 
}

class Polygon {
 constructor(height, width) {
  this.name = 'Polygon';
  this.height = height;
  this.width = width;
 }
}

class Square extends Polygon {
 constructor(length) {
  super(length, length);
  this.name = 'Square';
 }
}