class Human {
  get fullName() {
    return this.firstName + this.lastName;
  }
};

class Developer extends Human {
  constructor(firstName, lastName) {
    this.firstName = firstName;
    this.lastName = lastName;
  }

  get fullName() {
    // Template strings
    return super.fullName;
  }
}

new Developer('Stefan', 'Penner').fullName // should be: 'Stefan Penner' but is 'null'