[Fixed] Express router : Router.use() requires a middleware function but got a Object

Issue

I know there are lot of questions in SO but none of them gave me a solution

routes/authentication/index.js

import { Router } from 'express'

const router = Router();

router.get('/', (_req, _res) => console.log("Works"))

// module.exports = router                    <-- this works
export default router                      // <-- this doesn't

constants.js

const ROUTES = {
    'AUTHENTICATION' : require('../routes/authentication')
}

export default ROUTES

and using it in app.js as

import express from 'express'
import connectDatabase from './connectDb';
import ROUTES from './constants';
const app = express();

if (process.env.NODE_ENV !== 'production') {
  require('dotenv').config();
}
connectDatabase()

app.get('/', (_req, res) => {
  res.send("hello world")
})

app.use('/auth', ROUTES.AUTHENTICATION)

export default app;

Now with module.exports = router works but export default router throws an error

TypeError: Router.use() requires a middleware function but got a Object

I tried finding the cause for the problem but couldn’t.
Thanks in advance

Solution

You require the router file in constants.js, hence module.exports works.

For export default router to work, you need to import it.