create subclass in javascript

class.js

var Person = function(name) {
  this.name = name;
};
Person.prototype.isHuman = true;

// subclass
var Boy = class Boy extends Person {
  constructor(name, age) {
    super(name);
    this.age = age;
  }
  get sex() {
    return "M";
  }
};
// use getter or prototype.property
// Boy.prototype.sex = "M";

var Peter = new Boy("Peter", 13);
console.log(Peter.name); // "Peter"
console.log(Peter.age); // 13
console.log(Peter.sex); // "M"
console.log(Peter.isHuman); // true

constructor.js

var Person = function(name) {
  this.name = name;
};
Person.prototype.isHuman = true;

// subclass
var Boy = function(name, age) {
  Person.call(this, name); // 1
  this.age = age;
};
Boy.prototype = Object.create(Person.prototype); // 2
Boy.prototype.constructor = Boy; // 3
Boy.prototype.sex = "M";

var Peter = new Boy("Peter", 13);
console.log(Peter.name); // "Peter"
console.log(Peter.age); // 13
console.log(Peter.sex); // "M"
console.log(Peter.isHuman); // true