classObject.js

class Book {
  constructor(author, isbn, genre) {
    this.author = author;
    this.isbn = isbn;
    this.genre = genre;
  }
  getDescription() {
    return this.author+' '+this.isbn+' '+this.genre;
  }
}

class Adventure extends Book {
  constructor(author, isbn, genre, price) {
    super(author, isbn, genre);
    this.price = price;
  }
  getDescription() {
    return super.getDescription() + ' ' + this.price;
  }
}

let book = new Book('Fundamentals of Javascript', 'BA1234UX09', 'Herbert Shin');

console.log(book.author);
console.log(book.getDescription());

let adventure = new Adventure('Around the world in 80 days', 'YT46582BNH', 'Jules Verne', 7.99);

console.log(adventure.getDescription());