对象作为javaScript中的模型[关闭]

class Library {
    constructor(name) {
        this.name = name;
        this.books = []; // Instantiate the books array.
    }
    addBook(book) {
        this.books.push(book);
        // Some extra handling if a book can only be in one library
        if (book.library) book.library.removeBook(book);
        book.library = this; 
    }
    removeBook(book) {
        let i = this.books.indexOf(book);
        if (i === -1) return;
        this.books.splice(i, 1);
        book.library = null;
    }
    getBooksList() {
        return this.books;
    }
}

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

const book = new Book("1984", "George Orwell");
const library = new Library("The London Library");
library.addBook(book);
console.log("The book " + book.title + " is in " + book.library.name);

const otherLibrary = new Library("The Library of Birmingam");
otherLibrary.addBook(book);
console.log("The book " + book.title + " is in " + book.library.name);