Router.use() requires middleware function but got a undefined

because you are exporting module with a function inside so you need to return your router at the end of your function at division_model.js

return router;

this should work

You must return a router in your middleware here:

app.use('/division', division_model);

So, your module export function should end with:

return router;

You also have conflicting ideas when setting this up. If you want the app to define the route as /division which you do here:

app.use('/division', division_model);

then you do not need to redefine the route again like you do here:

var router = express.Router();
router.route('/division');

You can simply:

app.use(division_model);

-- or --

/**
 * division_model.js
 */
var router = express.Router();
router.route('/');
//omitting route code
router.route('/:division_id');
//omitting route code

return router;

/**
 * server.js
 */

app.use('/division', division_model);