12.1 在网页应用中管理用户
JavaScript中的面向对象编程（OOP）允许创建复杂、可扩展且易于维护的应用。下面是一些在JavaScript中使用OOP的实际例子，包括类、继承、封装和多态。
想象一下，我们在开发一个用于管理用户的网页应用。我们可以为不同类型的用户创建类，比如User、Admin和Guest，利用继承来创建专门的类。
解释：
User类包含login和logout方法Admin类继承自User，并添加了deleteUser方法Guest类继承自User，并添加了requestAccess方法Admin和Guest类的实例使用自己类和基类的方法
代码：
JavaScript
class User {
constructor(username, email) {
this.username = username;
this.email = email;
}
login() {
console.log(`${this.username} logged in.`);
}
logout() {
console.log(`${this.username} logged out.`);
}
}
class Admin extends User {
constructor(username, email) {
super(username, email);
this.role = 'admin';
}
deleteUser(user) {
console.log(`${this.username} deleted user ${user.username}.`);
}
}
class Guest extends User {
constructor(username, email) {
super(username, email);
this.role = 'guest';
}
requestAccess() {
console.log(`${this.username} requested access.`);
}
}
const admin = new Admin('adminUser', 'admin@example.com');
const guest = new Guest('guestUser', 'guest@example.com');
admin.login(); // "adminUser logged in."
admin.deleteUser(guest); // "adminUser deleted user guestUser."
admin.logout(); // "adminUser logged out."
guest.login(); // "guestUser logged in."
guest.requestAccess(); // "guestUser requested access."
guest.logout(); // "guestUser logged out."
12.2 管理在线商店的商品
在这个例子中，我们将创建类来表示在线商店中的不同类型商品，如Product、Electronics和Clothing。我们还将实现多态来处理calculateDiscount方法。
解释：
Product类包含calculateDiscount方法，默认计算10%的折扣Electronics类重写了calculateDiscount方法，为电子产品提供20%的折扣Clothing类重写了calculateDiscount方法，为服装提供15%的折扣Electronics和Clothing类的实例使用它们自己的calculateDiscount方法计算折扣
代码：
JavaScript
class Product {
constructor(name, price) {
this.name = name;
this.price = price;
}
calculateDiscount() {
return this.price * 0.1; // 默认10%折扣
}
display() {
console.log(`${this.name} - $${this.price.toFixed(2)}`);
}
}
class Electronics extends Product {
constructor(name, price, brand) {
super(name, price);
this.brand = brand;
}
calculateDiscount() {
return this.price * 0.2; // 电子产品20%折扣
}
}
class Clothing extends Product {
constructor(name, price, size) {
super(name, price);
this.size = size;
}
calculateDiscount() {
return this.price * 0.15; // 服装15%折扣
}
}
const laptop = new Electronics('Laptop', 1000, 'BrandX');
const tshirt = new Clothing('T-Shirt', 20, 'M');
laptop.display(); // "Laptop - $1000.00"
console.log(`Discount: $${laptop.calculateDiscount().toFixed(2)}`); // "Discount: $200.00"
tshirt.display(); // "T-Shirt - $20.00"
console.log(`Discount: $${tshirt.calculateDiscount().toFixed(2)}`); // "Discount: $3.00"
12.3: 管理图书馆
在这个例子中，我们将创建类来管理图书馆，包括Book、Magazine和Library类。我们还将实现添加和删除库中元素的方法。
解释：
Book和Magazine类继承自LibraryItem类，并重写了display方法Library类管理图书馆项目的集合，提供addItem、removeItem和displayItems方法Book和Magazine类的实例被添加到和从图书馆中移除，其信息通过display方法显示
代码：
JavaScript
class LibraryItem {
constructor(title, year) {
this.title = title;
this.year = year;
}
display() {
console.log(`${this.title} (${this.year})`);
}
}
class Book extends LibraryItem {
constructor(title, year, author) {
super(title, year);
this.author = author;
}
display() {
console.log(`${this.title} by ${this.author} (${this.year})`);
}
}
class Magazine extends LibraryItem {
constructor(title, year, issueNumber) {
super(title, year);
this.issueNumber = issueNumber;
}
display() {
console.log(`${this.title} - Issue ${this.issueNumber} (${this.year})`);
}
}
class Library {
constructor() {
this.items = [];
}
addItem(item) {
this.items.push(item);
console.log(`Added: ${item.title}`);
}
removeItem(title) {
this.items = this.items.filter(item => item.title !== title);
console.log(`Removed: ${title}`);
}
displayItems() {
this.items.forEach(item => item.display());
}
}
const library = new Library();
const book = new Book('JavaScript: The Good Parts', 2008, 'Douglas Crockford');
const magazine = new Magazine('JavaScript Weekly', 2021, 450);
library.addItem(book); // "Added: JavaScript: The Good Parts"
library.addItem(magazine); // "Added: JavaScript Weekly"
library.displayItems();
// "JavaScript: The Good Parts by Douglas Crockford (2008)"
// "JavaScript Weekly - Issue 450 (2021)"
library.removeItem('JavaScript Weekly'); // "Removed: JavaScript Weekly"
library.displayItems(); // "JavaScript: The Good Parts by Douglas Crockford (2008)"
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