ES6 Router.use() requires a middleware function but got a Object - express

Question

Now I worked with Node.js + Express to make some api server.
I installed babel-preset-latest to use ES6 statement.
However, When I write some code, it throws error ->
Router.use() requires a middleware function but got a Object
[index.js]
import express from 'express';
import bodyParser from 'body-parser';
const app = express();
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));
app.get('/', (req, res) => {
res.send('main');
});
app.use('/api', require('./api/auth'));
app.listen(3000, () => {
console.log("Express Running port 3000")
})
[/api/auth/index.js]
import express from 'express';
const router = express.Router();
router.get('/', (res, req) => {
res.send('auth main')
});
export default router;
In ES6, module.export can replace to export.
But it throw errors. So, after I replace export default router; to module.exports = router;, It works perfectly.
Why do I get this error? Is there any syntax error?
Thanks.

Answer 1

[SOLVED]
[index.js]
import express from 'express';
import bodyParser from 'body-parser';
import authRouter from './api/auth';
const app = express();
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));
app.get('/', (req, res) => {
res.send('main');
});
app.use('/api', authRouter);
app.listen(3000, () => {
console.log("Express Running port 3000")
})
[/api/auth/index.js]
import express from 'express';
const router = express.Router();
router.get('/', (res, req) => {
res.send('auth main')
});
export default router;
in index.js, Define import statement -> import authRouter from './api/auth';
and replace app.use('/api', require('./api/auth');
to
app.use('/api', authRouter);