What are the advantages of applying dependency injection in real projects?

Dependency Injection (DI) helps make code more modular and testable. In real projects, it provides several advantages:

• Improved testability: dependencies can be easily replaced with mocks or stubs during testing.
• Loose coupling of components: classes and modules do not create dependencies themselves but receive them from outside, making it easier to replace and update components.
• Increased reusability: components become more versatile as they do not depend on specific implementations.
• Simplified dependency management: centralized management of dependencies simplifies configuration and scaling of the application.

Example in Node.js using a simple DI container:

class Logger {
  log(message) {
    console.log(message);
  }
}

class UserService {
  constructor(logger) {
    this.logger = logger;
  }

  createUser(name) {
    this.logger.log(`User ${name} created`);
  }
}

const logger = new Logger();
const userService = new UserService(logger);
userService.createUser('Alice');

Here, UserService does not create Logger itself but receives it from outside, which simplifies replacing the logger, for example, with a test logger.