Question

我正在创建一个包含三个类的数字图书馆：Library，Shelf＆amp;书。货架上的内容是一系列书籍。书籍有两种方法，enshelf和unshelf。当一本书被取消保存时，它应该从它所在的架子上设置删除它自己的实例，然后将它的location属性设置为null。如何修改它所坐的架子？在构造函数中，如果我更改this.location，它将只给该属性一个新值，而不是修改它指向的变量。我觉得这很简单，我忽略了一些非常基本的东西。

var _ = require('lodash');

//books
var oldMan = new Book("Old Man and the Sea", "Ernest Hemingway", 0684801221);
var grapes = new Book("The Grapes of Wrath", "John Steinbeck", 0241952476);
var diamondAge = new Book("The Diamond Age", "Neal Stephenson", 0324249248);

//shelves
var shelf0 = new Shelf(0);
var shelf1 = new Shelf(1);

//libraries
var myLibrary = new Library([shelf0, shelf1], "123 Fake Street");

//these need to accept an unlimited amount of each
function Library(shelves, address) {
    this.shelves = shelves; //shelves is an array
    this.address = address;
    this.getAllBooks = function() {
        console.log("Here are all the books in the library: ");
        for (var i = 0; i < this.shelves.length; i++) {
            console.log("Shelf number " + i + ": ");
            for (var j = 0; j < this.shelves[i].contents.length; j++) {
                console.log(this.shelves[i].contents[j].name);
            }
        }
    }
}

function Shelf(id) {
    this.id = id;
    this.contents = [];
}

function Book(name, author, isbn) {
    this.name = name;
    this.author = author;
    this.isbn = isbn;
    this.location = null;
    this.enshelf = function(newLocation) {
        this.location = newLocation;
        newLocation.contents.push(this);
    }
    this.unshelf = function() {
        _.without(this.location, this.name); //this doesn't work
        this.location = null;
    }
}


console.log("Welcome to Digital Library 0.1!");

oldMan.enshelf(shelf1);
myLibrary.getAllBooks();
oldMan.unshelf();
myLibrary.getAllBooks();

Answer 1

使用unshelf方法的小问题，很容易解决：

this.unshelf = function() {
    this.location.contents = 
        _.without(this.location.contents, this);
    this.location = null;
}

但请注意，shelf和unshelf应该是Shelf的方法，而不是Book的方法。此外，如果您必须使用此方法，请使用警卫包围它，如下所示：

this.unshelf = function() {
    if (this.location) {
      this.location.contents = 
          _.without(this.location.contents, this);
      this.location = null;
    }
}

Answer 2

一些小问题：

without适用于数组并返回数组的副本，其中删除了元素 - 原始内容未受影响。因此，您需要传递location.contents而不仅仅是location ，并且将其重新分配回location.contents。

此外，您将整本书添加到书架，然后尝试按名称删除它，因此它不匹配并被删除。所以只需将this传递给without：

this.unshelf = function() {
    if (this.location) {
        this.location.contents = _.without(this.location.contents, this);
        this.location = null;
    }
}

Javascript：从指针修改对象

2 个答案: