Factory Function Injection

server.js

const MongoClient = require('mongodb').MongoClient

const Controller = require('./controller')
const Service = require('./service')
const Repository = require('./repository')

MongoClient.connect('some mongo url')
  .then((db) => {
    const repository = Repository(db)
    const service = Service(repository)
    const controller = Controller(service)
    
    controller.doTheThing()
  })
  .catch(console.log)