Can you give an example of how you applied SOLID principles in real projects?

In real Node.js projects, I applied SOLID principles to improve code structure and facilitate maintenance.

For example, the Single Responsibility principle helped separate HTTP request handling logic and business logic into different modules:

// userController.js
class UserController {
  constructor(userService) {
    this.userService = userService;
  }

  async getUser(req, res) {
    const user = await this.userService.findUser(req.params.id);
    res.json(user);
  }
}

// userService.js
class UserService {
  async findUser(id) {
    // database access logic
  }
}

I also used the Dependency Inversion principle by passing dependencies through the constructor, which made testing and component replacement easier.

This increased modularity and made scaling the application easier.