Flyweight example fix

flyweight-fix.js

class Book {
    constructor(title, author, isbn) {
        this.title = title;
        this.author = author;
        this.isbn = isbn;
    }
}

const isbnNumbers = new Set();
const bookList = [];
const sharedInstances = [];

const addBook = (title, author, isbn, availibility, sales) => {
    const bookSharedInstance = createBook(title, author, isbn)

    const book = {
        sales,
        availibility,
        isbn,
        __proto__: bookSharedInstance
    };

    bookList.push(book);
    return book;
};


const createBook = (title, author, isbn) => {
    const book = isbnNumbers.has(isbn);

    if (book) {
        return getSharedBookInstance(title);
    } else {
        const book = new Book(title, author, isbn);
        isbnNumbers.add(isbn);
        sharedInstances.push(book)
        return book;
    }
};

const getSharedBookInstance = (title) => {
    return sharedInstances.filter(book => book.title === title)[0]
}

const getBooks = (title) => {
    return bookList.filter(book => book.title === title)
}

addBook("Harry Potter", "JK Rowling", "AB123", false, 100);
addBook("Harry Potter", "JK Rowling", "AB123", true, 50);
addBook("To Kill a Mockingbird", "Harper Lee", "CD345", true, 10);
addBook("To Kill a Mockingbird", "Harper Lee", "CD345", false, 20);
addBook("The Great Gatsby", "F. Scott Fitzgerald", "EF567", false, 20);

console.log("Total amount of copies: ", bookList.length);
console.log("Total amount of books: ", isbnNumbers.size);


const harryPotterBooks = getBooks("Harry Potter")
console.log("Books:", harryPotterBooks.length)

const [firstBook, secondBook] = harryPotterBooks

console.log("Are objects equal:", firstBook === secondBook)
console.log("Do they share the same prototype:", Object.getPrototypeOf(firstBook) === Object.getPrototypeOf(secondBook))