如何从类方法返回正确值？JS类方法逻辑错误排查求助

我知道这个问题对大多数人来说可能很简单，但我已经卡了一整天。我觉得问题出在setCurrent(book)或者finishCurrentBook方法里。

功能要求 #

setCurrent(book) – 将指定书籍设为图书馆当前阅读书籍，将该书籍的currentBook字段设为true，返回"You just started reading: Book_name"。如果该书籍已是当前阅读书籍，返回"You are already reading: Book_name"。若当前书籍未读完就尝试设置另一本为当前书籍，返回"You can't add this book as the current book before finishing: currentBook_name"。同一时刻图书馆只能有一本当前阅读书籍。

finishCurrentBook() – 将当前阅读书籍标记为已读，将最近读完的书籍设为刚完成的这本，将当前书籍的currentBook字段设为false。若未定义currentBook，返回消息"You're not reading any book right now..."。

问题现状 #

测试代码不可修改，预期输出true、false，但实际得到undefined、undefined。允许修改类实现，但不能改动测试代码。

现有代码 #

class Book {
  constructor(title, genre, author) {
    this.title = title;
    this.genre = genre;
    this.author = author;
    this.finishedRead = false;
  }
}
class Library {
  constructor(name) {
    this.name = name;
    this.allBooks = [];
    this.currentBook = false;
    this.lastBook = null;
  }

  getAllBooks() {
    return this.allBooks;
  }

  getCurrentBook() {
    if (this.currentBook) {
      return `You are currently reading: ${this.currentBook.title}`;
    } else {
      return "You're not reading any book at the moment";
    }
  }

  getLastBook() {
    if (this.lastBook) {
      return `The last book you read was: ${this.lastBook.title}`;
    } else {
      return "You haven't read anything in a while!";
    }
  }

  getBooksToRead() {
    return this.allBooks.filter((book) => !book.finishedRead).length;
  }

  getFinishedBooks() {
    const finishedBooks = this.allBooks.filter((book) => book.finishedRead);
    if (finishedBooks.length > 0) {
      return finishedBooks;
    } else {
      return 'You have not yet read any books from your library!';
    }
  }

  addBook(book) {
    this.allBooks.push(book);
  }

  setCurrent(book) {
    if (this.currentBook === book) {
      return `You are already reading: ${book.title}`;
    } else if (this.currentBook) {
      return `You can't add this book as the current book before finishing: ${this.currentBook.title}`;
    } else {
      this.currentBook = book;
      book.finishedRead = false; // Ensure the book is marked as unread
      return `You just started reading: ${book.title}`;
    }
  }

  finishCurrentBook() {
    if (this.currentBook) {
      this.currentBook.finishedRead = true;
      this.lastBook = this.currentBook;
      this.currentBook = null;
      return `You have finished reading: ${this.lastBook.title}`;
    } else {
      return "You're not reading any book right now...";
    }
  }
}

// 不可修改的测试代码
const myLibrary = new Library("My books");
const javaScript = new Book("JS", "IT", "Flanagan");
const winds = new Book("Winds", "Historical", "Hannah");
const ring = new Book("The Ring", "Fantasy ", "Tolkien");

const booksList = [javaScript, winds, ring];
booksList.forEach((b) => myLibrary.addBook(b));

myLibrary.setCurrent(ring);
console.log(ring.currentBook);
myLibrary.finishCurrentBook();
console.log(ring.currentBook);

解决方案 #

问题核心是没有按照功能要求操作Book实例的currentBook字段，现有代码只处理了finishedRead，完全忽略了currentBook的设置。

修改步骤： #

1. 初始化Book类的currentBook字段，避免初始值为undefined：

class Book {
  constructor(title, genre, author) {
    this.title = title;
    this.genre = genre;
    this.author = author;
    this.finishedRead = false;
    this.currentBook = false; // 新增：初始化currentBook为false
  }
}

2. 修改setCurrent方法，在设置当前书籍时，将书籍的currentBook设为true：

setCurrent(book) {
  if (this.currentBook === book) {
    return `You are already reading: ${book.title}`;
  } else if (this.currentBook) {
    return `You can't add this book as the current book before finishing: ${this.currentBook.title}`;
  } else {
    this.currentBook = book;
    book.finishedRead = false;
    book.currentBook = true; // 新增：标记该书籍为当前阅读状态
    return `You just started reading: ${book.title}`;
  }
}

3. 修改finishCurrentBook方法，在完成阅读时，将书籍的currentBook设为false：

finishCurrentBook() {
  if (this.currentBook) {
    this.currentBook.finishedRead = true;
    this.currentBook.currentBook = false; // 新增：取消该书籍的当前阅读标记
    this.lastBook = this.currentBook;
    this.currentBook = null;
    return `You have finished reading: ${this.lastBook.title}`;
  } else {
    return "You're not reading any book right now...";
  }
}

修改后运行测试代码，console.log会依次输出true和false，符合预期。

内容的提问来源于stack exchange，提问作者antonkornilov-ua