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Api : Express : throw new TypeError('Router.use() requires a middleware function but got a ' + gettype(fn))

I have just started with api building using express but getting below error.
below is my code. please help.
Server.js code
const express = require('express');
const mongoose = require('mongoose')
const users = require('./routes/api/users');
const profile = require('./routes/api/profile');
const posts = require('./routes/api/posts');
const app = express();
//DB config
const db = require('./config/keys').mongoURI;
//connet to MongoDB
mongoose
.connect(db)
.then(() => console.log('MongoDB connected'))
.catch(err => console.log(err));
app.get('/', (req, res) => res.send('Hello Ajas Bakran'));
//Use Routes
app.use('/api/users', users);
app.use('/api/profile', profile);
app.use('/api/posts', posts);
const port = process.env.PORT || 5000;
app.listen(port, () => console.log(`Server running on port ${port}`));
users.js code
const express = require('express');
const router = express.Router();
router.get('/test', (req, res) => res.json({msg:'Hello Users'}));
module.exports = router;
profile.js code
const express = require('express');
const router = express.Router();
router.get('/test', (req, res) => res.json({msg:'Hello profile'}));
module.exports = router;
posts.js
const express = require('express');
const router = express.Router();
router.get('/test', (req, res) => res.json({msg:'Hello posts'}));
module.exports = router;
I refered few answers on stackoverflow, but moslty solution to that was having module.exports = router; this line at the end. but i do have the line present already still i get the same error. Really not sure what is going wrong

From what I can see I think you need to re-write this portion:
router.route('/')
instead of
router.get
Usually these types of error originate from non properly exported router.

import modules in nodejs routes

I have declared socket.io in index.js file, And I would pass soket object to route module.
const express = require('express');
const app = express();
var bodyParser = require('body-parser');
var mongoose = require('mongoose');
var MongoClient = require('mongodb').MongoClient;
var server = require('http').Server(app);
var io = require('socket.io')(server);
var routes = require('./routes/routes')(io);
const dbb = mongoose.connect("mongodb://xxx:xxx#ds137600.mlab.com:37600/tasksdb");
var db = mongoose.connection;
db.on('error', console.error.bind(console, 'connection error:'));
app.use('/', routes);
var server= app.listen(3000, function () {
console.log('Example app listening on port 3000!')
})
routes.js
var express = require("express"); // call express
var taskSchema = require("../models/taskModel");
var mongoose = require("mongoose");
var router = express.Router(); // get an instance of the express Router
router
.route("/tasks")
.post(function (req, res, next) {
....
});
router
.route("/tasks")
.get(function (req, res) {
....
});
module.exports = router;
How can I transfert it to routes.js? what are the different ways to do it ? I still not well understanding how modules works

For server:
const app = express();
app.use(logger('tiny'));
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({extended: false}));
app.use((req, res, next) => {
const origin = req.headers.origin;
if (allowed_header.indexOf(origin) > -1) {
res.header('Access-Control-Allow-Origin', origin);
}
res.header(
'Access-Control-Allow-Headers',
'Origin, X-Requested-With, Content-Type, gutsyJwt, Accept'
);
next();
});
app.io = require('socket.io')({
origins: ['*:*'],
});
require('./routes')(app);
module.exports = app;
Then in route:
module.exports = app => {
app.post('/api/bar', (req, res) =>
fooController.bar(req, res, app.io)
);
};
Then in controller:
module.exports = {
bar(req, res, io) {
io.emit('message', req.body.message);
res.status(200).send({msg: 'Message broadcasted!'});
},
};
In this post, it is asking the similar question as well if you need more reference.
ExpressJS how do I pass objects with state (eg. connections)?

Express subrouter returns 404

I have this router (http/api/ping.js):
var express = require('express');
var router = express.Router();
router.get('/ping', function (req, res) {
res.send("You called /api/ping");
});
module.exports = router;
This router is embedded into this router (http/api/index.js):
var express = require('express');
var router = express.Router();
router.get('/', function (req, res) {
res.send('You called /api');
});
router.use('/ping', require('./ping'));
module.exports = router;
And this router is used by my Express.js app (app.js):
var http = require('http');
var express = require('express');
var bodyParser = require('body-parser');
var logger = require('./config').logger;
// Create app
var app = express();
var server = http.createServer(app)
var io = require('socket.io')(server);
// App config
app.use(bodyParser.json());
app.use('/api', require('./http/api'));
// Display requests on console
app.use(function (req, res, next) {
logger.trace(req.method, req._parsedUrl.href);
next()
});
module.exports = {
app: app,
server: server
};
When I run the app, /api returns You called /api, but /api/ping gives me a 404.
I am using Node 6.9.1 and Express ^4.14.0

I think order matters in this scenario. Try putting /ping above the / get route.
router.use('/ping', require('./ping'));
router.get('/', function (req, res) {
res.send('You called /api');
});
Also in your ping route you say the path to your route is /ping you also say it is /ping when you import it to the other router, which would make the path /api/ping/ping
change
router.get('/ping', function (req, res) {
res.send("You called /api/ping");
});
to
router.get('/', function (req, res) {
res.send("You called /api/ping");
});

I think your routing is incorrect on this line
router.use('/ping', require('./ping'));
this will point to http/api/ping/ping
it should be
router.use('/', require('./ping'));

Cannot import my routes module

When I try to import my routes module into the main app with app.use(require(./routes)) I get app.use() requires middleware functions. How should I go about the module.exports function to make it work?
My routes:
var express = require('express'),
auth = require('../middleware/auth.js'),
user = require('../models/user.js'),
formidable = require('formidable');
module.exports = (function () {
app.post('/', function (req, res) {
var form = new formidable.IncomingForm();
form.parse(req, function (err, fields, files) {
user.create(fields.username, fields.email, fields.password);
});
res.render('./game/game.html', {});
});
app.get('/', function (req, res) {
res.render('./index.html', {});
});
app.get('/game', function (req, res) {
res.render('/views/index.html');
});
})();
My main app.js:
var express = require('express'),
app = require('express')(),
cookieSession = require('cookie-session'),
ejs = require('ejs'),
path = require('path'),
cookieParser = require('cookie-parser'),
util = require('util'),
port = process.env.PORT || 3000,
auth = require('./middleware/auth.js'),
user = require('./models/user.js'),
formidable = require('formidable');
router = express.Router();
app.use(express.static(path.join(__dirname, 'public')));
app.set('views', __dirname + '/views');
app.engine('html', require('ejs').renderFile);
app.set('view engine', 'html');
//won't import routes
app.use(require('./routes'));
module.exports = router;
app.listen(port);

You need to return app in your exports function
module.exports = function (express) {
var app = express.Router();
app.post('/', function (req, res) {
var form = new formidable.IncomingForm();
form.parse(req, function (err, fields, files) {
user.create(fields.username, fields.email, fields.password);
});
res.render('./game/game.html', {});
});
app.get('/', function (req, res) {
res.render('./index.html', {});
});
app.get('/game', function (req, res) {
res.render('/views/index.html');
});
return app
};
......
app.use(require('./routes')(express));

Your routes need to be an instance of Express Router.
var express = require('express');
var router = express.Router();
router.get('/', function(req, res, next) {
res.send(req.headers);
});
module.exports = router;
Now in your app.js you can use them as following:
app.use('/', require('./routes/index'));

Your module should either mutate your router (app), or create its own router and export it.
Solution 1
Module
module.exports = function(app) {
app.post(...);
app.get(...);
}
Main app
require("./routes")(app)
Solution 2
Module
var app = express.Router();
app.post(...);
app.get(...);
module.exports = app;
Main app
app.use(require("./routes"))
Solution 2 is better in my opinion because it avoids mutation.

Router.use requires middleware function?

So I'm trying to seperate my login routes in a seperate JS file called login_routes.js
I keep getting this specific error:
TypeError: Router.use() requires middleware function but got a Object
at Function. (/Users/ethanthomas/Desktop/mean-stuff/express-server/node_modules/express/lib/router/index.js:446:13)
Not entirely understanding what it's asking me to implement?
login_routes.js:
var express = require('express');
var app = express();
app.route('/login')
.get(function(req, res, next) {
res.send('this is the login form');
})
.post(function(req, res, next) {
console.log('processing');
res.send('proccessing the login form!');
});
server.js:
var express = require('express');
var app = express();
var path = require('path');
var adminRoutes = require('./app/routes/admin_routes');
var loginRoutes = require('./app/routes/login_routes');
app.use('/admin', adminRoutes);
app.use('/login', loginRoutes);
//send our index.html file to the user for the home page
app.get('/', function(req, res) {
res.sendFile(path.join(__dirname + '/index.html'));
});
//start the server
app.listen(1337);
console.log('leet is the magic port');

Your login_routes.js should look something like this (in the context of express):
var express = require('express');
var router = express.Router();
// GET request to /login
router.get('/', function(req, res, next) {
// do something
});
// POST request to /login
router.post('/', function(req, res, next) {
// do something
});
module.exports = router;
In your app.js you use
var login_routes = require('./login_routes');
...
app.use('/login', login_routes);
...
Have a look at the code generated by the express-generator module. That is a starting point for express webserver apps.

People have already offered hints at the solution in comments.
The first issue is that you need to export your "sub" app from login_routes.js. To do so, change this:
var app = express();
Into this:
var app = module.exports = express();
Secondly, you are—probably unintentionally—creating routes for GET /login/login and POST /login/login. To solve this, use this in login_routes.js:
app.route('/').get(...).post(...);
This is because the root path in your sub app (the one in login_routes.js) will get mapped to the path used in app.use() in your main app (server.js).

Do like this:
login_routes.js:
exports.get = function( req, res ) {
res.send('this is the login form');
};
exports.post = function( req, res ) {
console.log('processing');
res.send('proccessing the login form!');
};
server.js:
var loginRoutes = require('./app/routes/login_routes');
app.get('/login', loginRoutes.get);
app.put('/login', loginRoutes.post);

login_routes.js:
var express = require('express');
var app = express();
app.route('/login')
.get(function(req, res, next) {
res.send('this is the login form');
})
.post(function(req, res, next) {
console.log('processing');
res.send('proccessing the login form!');
});
module.exports = router;
just writ module.exports = router then it will be work