In your sample code, you must just send a response to the client by res.json() or res.end() :

const express = require('express');
const multer = require('multer');
const upload = multer({ dest: 'uploads/' });

const app = express();

app.post('/profile', upload.single('avatar'), function (req, res, next) {
  // req.file is the `avatar` file
  // req.body will hold the text fields, if there were any

  res.status(204).end();
});

app.post('/photos/upload', upload.array('photos', 12), function (req, res, next) {
  // req.files is array of `photos` files
  // req.body will contain the text fields, if there were any

  res.status(204).end();
});

i can give you an example of how i implemented an imageupload in my app. it the code to upload a profile image for a user. i am also using multer middleware so it shoulder be similiar for you:

code is as follows:

// multer middleware:
const multer = require('multer');

const MIME_TYPE_MAP = {
  'image/png': 'png',
  'image/jpeg': 'jpg',
  'image/jpg': 'jpg',
};

module.exports = storage = multer.diskStorage({
  destination: (req, file, cb) => {
    const isValid = MIME_TYPE_MAP[file.mimetype];
    let error = new Error('invalid mime type');
    if (isValid) {
      error = null;
    }
    cb(error, 'images');
  },
  filename: (req, file, cb) => {
    const name = file.originalname.toLowerCase().split(' ').join('-');
    const ext = MIME_TYPE_MAP[file.mimetype];
    if (name.includes('.' + ext)) {
      cb(null, name)
    } else {
      cb(null, name + '.' + ext);
    }
  },
});

and here the code in the service handling the fileupload

// profile service in backend written in express
exports.uploadImage = (req, res, next) => {
  const url = req.protocol + '://' + req.get('host');
  profileRepository
    .findOne({ _id: req.params.id })
    .then((response) => {
      const fetchedUser = response;
      fetchedUser.imagePath = url + '/images/' + req.file.filename;
      profileRepository
        .updateOne({ _id: req.params.id }, fetchedUser)
        .then((response) => {
          return res.status(200).json({
            message: 'profileimage updated',
          });
        })
        .catch((error) => {
          return res.status(500).json({
            message: 'uploading image failed',
          });
        });
    })
    .catch((error) => {
      return res.status(404).json({
        message: 'fetching user failed',
      });
    });
};

then i use the middleware in my profile routes file like this:

// profile.routes.js
const express = require('express');
const ProfileController = require('./profileController');
const checkAuth = require('../middleware/checkAuth');
const router = express.Router();
const fileStorage = require('../middleware/fileStorage');
const multer = require('multer');
// imageUpload
router.post('/user/image/:id', checkAuth, multer({storage: fileStorage}).single('image'), ProfileController.image);

my Controller then calls the service function with the actual business logic like this:

// profile.controller.js
const profileService = require('./profileService');
exports.image = (req, res, next) => {
  return profileService.uploadImage(req, res);
};

and finally my route is used by my app.js file like this:

// app.js
const express = require('express');
const profileRoutes = require('./profile/profileRoutes');

const app = express();

// set images path for saving images on server
app.use('/images', express.static(path.join('images')));

app.use('/api', profileRoutes);

module.exports = app;

i hope i was able to point you in the right direction with my example