index.js

class DIContainer {
    constructor() {
        this.services = new Map();
        this.instances = new Map();
    }

    register(name, factory, dependencies = []) {
        this.services.set(name, { factory, dependencies });
    }

    resolve(name) {
        if (this.instances.has(name)) {
            return this.instances.get(name);
        }
        const service = this.services.get(name);
        if (!service) throw new Error(`Service ${name} not found`);
        const dependencies = service.dependencies.map(dep => this.resolve(dep));
        const instance = service.factory(...dependencies);
        this.instances.set(name, instance);
        return instance;
    }
}

class ConsoleLogger {
    log(message) {
        console.log(`[LOG] ${new Date().toLocaleTimeString()} - ${message}`);
    }
}

class EmailService {
    constructor(logger) { this.logger = logger; }
    sendEmail(to, subject, body) {
        this.logger.log(`Preparing email to: ${to}`);
        console.log(`Sending email to: ${to}`);
        console.log(`Subject: ${subject}`);
        console.log(`Body: ${body}`);
        this.logger.log(`Email sent to: ${to}`);
    }
}

class NotificationService {
    constructor(emailService, logger) {
        this.emailService = emailService;
        this.logger = logger;
    }
    sendWelcomeNotification(userEmail, userName) {
        this.logger.log(`Processing notification for: ${userName}`);
        this.emailService.sendEmail(userEmail, "Welcome!", `Hello ${userName}, welcome to our platform!`);
        this.logger.log("Notification completed");
    }
}

console.log("Email Notification DI Example Starting...\n");
const container = new DIContainer();
container.register('logger', () => new ConsoleLogger());
container.register('emailService', (logger) => new EmailService(logger), ['logger']);
container.register('notificationService', (emailService, logger) => new NotificationService(emailService, logger), ['emailService', 'logger']);

const notificationService = container.resolve('notificationService');
notificationService.sendWelcomeNotification("john@example.com", "John");
console.log("\nEmail Notification DI worked successfully!");