Javascript:从指针修改对象

Javascript: Modify an object from a pointer

本文关键字：修改 对象 指针 Javascript      更新时间：2023-09-26

我正在制作一个有三个类的数字图书馆：library、Shelf&书书架上摆放着一排本书。书有两种方法，入身和出身。当一本书被取消书架时，它应该设置从书架上删除它自己的实例，然后将它的位置属性设置为null。我该如何修改它所在的架子？在构造函数中，如果我更改this.location，它只会给这个属性一个新的值，而不是修改它所指向的变量。我觉得这真的很简单，我忽略了一些超级基本的东西。

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();

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;
}

然而，考虑shelf和unshelf应该是Shelf的方法，而不是Book的方法。此外，如果你必须有这种方法，用一个警卫包围它，就像这样：

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

几个小问题：

without处理数组，并返回已删除元素的数组副本-原始数组未被更改。因此，您需要传递location.contents，而不仅仅是location，并将其重新分配回location.contents。

此外，您将整本书添加到书架，然后尝试按名称删除它，这样它就不匹配并被删除。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;
    }
}
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