node.js设计模式下载

class Product {
    constructor(name) {
        this.name = name;
    }
}

class ProductFactory {
    createProduct(type) {
        switch (type) {
            case 'A':
                return new Product('Product A');
            case 'B':
                return new Product('Product B');
            default:
                throw new Error('Invalid product type');
        }
    }
}

const factory = new ProductFactory();
const productA = factory.createProduct('A');
console.log(productA.name); // 输出: Product A

class Database {
    constructor() {
        if (!Database.instance) {
            this.data = [];
            Database.instance = this;
        }
        return Database.instance;
    }

    addRecord(record) {
        this.data.push(record);
    }
}

const db1 = new Database();
db1.addRecord('Record 1');
const db2 = new Database();
console.log(db2.data); // 输出: ['Record 1']

class EventEmitter {
    constructor() {
        this.events = {};
    }

    on(event, listener) {
        if (!this.events[event]) {
            this.events[event] = [];
        }
        this.events[event].push(listener);
    }

    emit(event, ...args) {
        if (this.events[event]) {
            this.events[event].forEach(listener => listener(...args));
        }
    }
}

const emitter = new EventEmitter();
emitter.on('greet', name => console.log(`Hello, ${name}!`));
emitter.emit('greet', 'World'); // 输出: Hello, World!

const Module = (function() {
    let privateVar = 'I am private';

    function privateMethod() {
        console.log(privateVar);
    }

    return {
        publicMethod: function() {
            privateMethod();
        }
    };
})();

Module.publicMethod(); // 输出: I am private