DatabaseController in NodeJS MySQL with Typescript

Yes it's possible. I'm not entirely familiar with typescript so some psuedo code below. Untested.

Somewhere in another file, configure your database connection and the service:

import { MyConnection } from 'my-db-package';

class DatabaseService {
  private connection: MyConnection

  constructor(db: MyConnection) {
    this.connection = db;
  }

  // Return the promise if any.
  // Don't want to handle the error here.
  // Let your controller handle the error
  async openConnection() {
    return this.connection.open()
  }

  async closeConnection() {
    return this.connection.close()
  }

  async getAllUsers() {
    return this.connection.query('SELECT * FROM USERS;')
  }

}

export default DatabaseService;

import { Database } from 'my-db-driver'
import { DatabaseService } from 'my-db-service'

// Don't actually connect here
// Just create the object so it's ready for connection.
const connection = new Database({
  // config
})

// Wire up the internal db connection
// Remember this is a singleton.
export default new DatabaseService(connection)

Next wire up your controller with the new database service:

import { Request, Response } from 'express';
import { DatabaseService } from './my-service'

class UserController {
  private dbService: DatabaseService;

  constructor(dbService: DatabaseService) {
    this.dbService = dbService;
  }

  async connect() {
    return this.dbService.openConnection()
  }

  async close() {
    return this.dbService.closeConnection()
  }

  async getAllUsers(req: Request, res: Response) {
    let users

    try {
      users = await this.dbService.getAllUsers();
    } catch (error) {
      // ...
    }

    res.json(users)
  }

}

export default UserController;

Then hook up your routes:

import { express } from 'express'
import { UserController } from 'user-controller'
import { DatabaseService } from 'database-service'

const userController = new UserController(DatabaseService);
const router: express.Router = express.Router();

router.get('/users', userController.getAllUsers)
// ...

export default router

Finally, hook up your routes with the main Express app:

import { express } from 'express'
import { userRoutes } from 'user-routes'

const app = express()

app.use(userRoutes)
// ..

Again, the above code is untested and likely unusable. It is meant to give you an example of one approach. You may find a better way to do it, but that's the gist of it.