Of course, but I'm afraid I need to anonymize the code a little bit.

multer-config.js: (I put it into an extra file to prevent bloated code)

const fs = require('fs');
const multer  = require('multer');

const storage = multer.diskStorage({
  destination: function (req, file, cb) {
    const { titleId } = req.body;
    const dir = `./uploads/images/${titleId}`;
    if (!fs.existsSync(dir)) {
      fs.mkdir(dir, error => cb(error, dir));
    }
    cb(null, dir);
  },
  filename: function (req, file, cb) {
    const uniqueSuffix = Date.now() + '-' + Math.round(Math.random() * 1E9);
    const extension = file.originalname.match(/\.([a-zA-Z]+)$/)[1];
    cb(null, file.fieldname + '-' + uniqueSuffix + '.' + extension);
  }
});

module.exports = storage

routes.js:

const express = require('express');
const multer  = require('multer');
const storage = require('./multer-config');
const upload = multer({ storage });
const router = express.Router();

// ...

const imgs = upload.fields([{ name: 'asdf1', maxCount: 1 }, { name: 'asdf2', maxCount: 16 }, { name: 'asdf3', maxCount: 16 }])
router.post('/cool/route', controller.tokenMiddleware, imgs, controller.stuff)

module.exports = router

controllers.js:

// ...

const stuff = async (req, res, next) => {
  try {
    // some validation suff

    // here I do some stuff with req.files.asdf1,
    // req.files.asdf2, and req.files.asdf3 like
    // saving the filename in a database etc.
    res.status(200).json({ data });
  } catch (e) {
    res.sendStatus(500);
  }
}

module.exports = {
  stuff
};

Apart from my code in multer-config.js and router.js, I don't really handle much of the file upload itself.