Question

我正在使用三个类编写一个库（在ES6 Javascript中）：开放时间，书籍，书籍。和“主”类库（由以前的类组成）。

我得到的控制台错误如下：未捕获TypeError：无法在Books.set书籍[作为书籍]中设置undefined属性'undefined'。

错误发生在setter中的Books类中。

以下是代码：

'use strict';
//OO library (Classes: Libary, Book, WorkingHours)
class WorkingHours{
    constructor(open, close, lunch){
        this.open = open;
        this.close = close;
        this.lunch = lunch;
    }
}
class Book {
    constructor(title, category, author){
        this.title = title;
        this.category = category;
        this.author = author;
    }
}
class Books {
    constructor(){
        this.books = [];
        //let books = new Array();
        //let books = [];
        var bookAmount = 0;
    }
    set books(book){
        //this.books.push(book);
        this.books[this.bookAmount] = book;
        this.bookAmount++;
    }
}
class Library { 
    constructor(workingHours, booksIn){
        this.workingHours = workingHours;
        this.booksIn = booksIn;
    }

    get workingHours() {
        return this.workingHours;
    }
    get booksIn() {
        return this.booksIn;
    }
}

var workHour = new WorkingHours(900,1700,false);
var bookColl = new Books();
var newBook = new Book("Mastery", "Real Stories", "Robert Greene");
bookColl.books = newBook;
newBook = new Book("48 Laws of Power", "Slef-teaching", "Robert Greene");
bookColl.books = newBook;
var newLib = new Library(workHour, bookColl);
console.log(newLib);

Answer 1

var bookAmount = 0没有初始化属性。 this.books = []导致books数组通过books setter分配，与在类外分配的方式相同，this.books[this.bookAmount] = ...使用books和{{1}进行评估未定义。

应该是：

bookAmount

class Books { constructor(){ this._books = []; this.bookAmount = 0; } ... }值是多余的，因为它已作为bookAmount提供。正确的方法是：

this._books.length

OO Javascript：数组未初始化

1 个答案: