Experiments with ES6 class syntax and private members (through Babel0

gistfile1.js

class Person {

  constructor(options) {
    
    this.firstname = options.firstname;
    this.lastname = options.lastname;
    Person.privateData.set(this, { dob: options.dob });
  }

  get fullname() {
    return this.firstname + ' ' + this.lastname;
  }

  greet() {
    console.log('Hello my name is ' + this.fullname);
  }
  
  sayAge() {
    console.log('I am ' + Person.calculateAge(Person.privateData.get(this).dob) + ' years old');
  }
  
  static calculateAge(dob) {
    var ageDate = new Date(Date.now() - dob.getTime()); // miliseconds from epoch
    return Math.abs(ageDate.getUTCFullYear() - 1970);
  }
  
  static privateData = new WeakMap();
}

class Customer extends Person {
    constructor(options) {
      super(options); 
    }
}

var andy = new Person({
  'firstname': 'Andy',
  'lastname': 'Polhill',
  'dob': new Date('12/13/1979')
});

var charles = new Person({
  'firstname': 'Charles',
  'lastname': 'Dickens',
  'dob': new Date('2/7/1812')
});

andy.greet();
andy.sayAge();
charles.greet();
charles.sayAge();
andy.dob = new Date('12/13/1986');
console.log(andy.dob)
andy.sayAge();

var sam = new Customer({
  'firstname': 'Sam',
  'lastname': 'Gray',
  'dob': new Date('05/10/1999')
});

sam.greet();