Example: overloaded controller

// AppController.ts

export class AppController {
  ...
  createUser (req: express.Request, res: express.Response): Promise<void> {
    // Get values from request
    const { username, email, password } = req.body;

    // Validate request values
    const isUsernameValid = TextUtils.isAtLeast(3, username) 
      && TextUtils.isAtMost(30, username);
    const isEmailValid = TextUtils.isValidEmail(email)
    const isPasswordValid = TextUtils.isAtLeast(3, password) 
      && TextUtils.isAtMost(25, password);

    // Check if username has already been taken
    const existingUserByUserName = await this.userRepo
      .getUserByUserName(username);

    if (existingUserByUserName) {
      return res.status(409).json({ 
        message: "Username already taken" 
      });
    }

    // Check if email already exists
    const existingUserByEmail = await this.userRepo
      .getUserByEmail(email);
    
    if (existingUserByEmail) {
      return res.status(409).json({ 
        message: "User already exists. Try logging in." 
      });
    }

    // Otherwise, create the user
    const user = await this.userRepo.create({
      username,
      email,
      password
    })

    // Send email verification email
    await this.emailService.sendVerificationEmaill(user.email);

    // Add email to mailing list
    await this.mailingList.add(user.email);
    
    // Do more stuff...
    ...
  }
}