Express server and socket.io not working in same port - node.js

Question

Not working can't find any issue in code##
If I put any port number instead of server it's working but why didn't it's working with socket server anyone explain
I tried some solution but none of them work I want to run socket.io and express on same port number
const express = require('express');
const cors = require("cors");
const socketIO = require('socket.io');
const http = require('http');
const app = express();
const server = http.createServer(app);
const passport = require("passport");
const authRoute = require('./routes/auth');
const userRoute = require('./routes/user');
const PORT = process.env.PORT || 9000;
const db = require('./config/mongoose');
app.use(express.json());
app.use(cors());
app.use(passport.initialize());
require("./config/passport")(passport);
app.use(express.json());
app.use("/api/auth", authRoute);
app.use("/api/user", passport.authenticate('jwt', { session: false }),userRoute);
if(process.env.NODE_ENV === 'production')
{
app.use(express.static('client/build'))
}
Here is the issue if I switch server to any port number it's fine
const io = socketIO(server, {
cors: {
origin: '*',
}
});
let state = {};
io.on("connection", (socket) => {
const { id } = socket.client;
socket.on('disconnect', function () {
console.log('socket disconnected!');
});
socket.on('join_room', function (data) {
console.log('joining request rec.', data);
socket.join(data.room);
io.in(data.room).emit('user_joined', data);
});
socket.on('send_code', function (data) {
io.in(data.room).emit('receive_code', data);
});
});
app.listen(PORT, function (err) {
if(err){
console.log(err);
return;
}
console.log(`Server is up and running on port: ${PORT}`);
});

Answer 1

http.createServer(app) and app.listen() are not compatible as they both try to do the same thing. If you look at the source code for app.listen(), you will see this:
app.listen = function listen() {
var server = http.createServer(this);
return server.listen.apply(server, arguments);
};
So, it's creating a DIFFERENT server object. You end up with two and the first one never gets started so when you give it to socket.io, it never works.
Instead, remove this:
const server = http.createServer(app);
And, use this instead:
const server = app.listen(PORT, function (err) { ...});
This way, your server variable will contain the one and only server object that is actually running.
Alternatively, you could remove the app.listen() and then just add this in it's place:
server.listen(PORT, ...);
The general idea is that you want this pair:
const server = http.createServer(app);
server.listen(PORT, ...);
Or, just this:
const server = app.listen(PORT, ...);
You cannot use both. Either way, that server object will represent the server that is actually running and will work with socket.io.