TypeError: Cannot read property 'use' of undefined Express

Question

I'm facing some issues with my express server when I use the 'app.use' command

in my task-routes.js file, I have the following code

import express from 'express';
const router = express.Router();


router.post('/task',(req, res) => {
    res.send('post.task - create a task');
});
router.get('/task',(req, res) => {
    res.send('get.task - get all tasks')
});
router.get('/task/:id',(req, res) => {
    res.send('get.task/:id - get task by id')
});
router.put('/task',(req, res) => {
    res.send('put.task - update a task')
});
router.delete('/task',(req, res) => {
    res.send('delete.task - delete a task')
});

export default router;

And in my routes.js file, I have this

import taskRoutes from './api/task/tasks-routes';

export function registerRoutes(app) {
app.use('/api',taskRoutes);

}

Index.js

import express from 'express';
const app = express()
import {registerRoutes} from './routes';
const port = 3000
registerRoutes();
app.get('/', (req, res) => res.send('Hello World!'))

app.listen(port, () => console.log(`MEVN app listening at http://localhost:${port}`))

This is the error I keep getting

/Users/musabhamid/Desktop/mevn-stack copy/prod-server/routes.js:15
  app.use('/api', _tasksRoutes2.default);
      ^

TypeError: Cannot read property 'use' of undefined
    at registerRoutes (/Users/musabhamid/Desktop/mevn-stack copy/prod-server/routes.js:15:7)
    at Object.<anonymous> (/Users/musabhamid/Desktop/mevn-stack copy/prod-server/index.js:14:28)

Answer 1

You are missing to pass app as argument at Index.js

import express from 'express';
const app = express()
import {registerRoutes} from './routes';
const port = 3000
registerRoutes(app); // <- Here
app.get('/', (req, res) => res.send('Hello World!'))

app.listen(port, () => console.log(`MEVN app listening at http://localhost:${port}`))

Answer 2

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

So you call app.use

What is app ?

 export function registerRoutes(app) {

It is the first argument you pass to registerRoutes .

So what is that?

 registerRoutes();

There isn't one. You didn't pass it an argument.

---

You have to pass the express object as the argument when you call the function.