index.js

const express = require('express');

const app = express();
const http = require('http').createServer(app);
const io = require('socket.io')(http);

app.use(express.static(__dirname));

// getting index.html file
app.get('/', (req, res) => {
    res.sendFile(__dirname + '/index.html');
});

const users = {};

io.on('connection', socket => {
    // If any new user joins, let other users connected to the server know!
    socket.on('new-user-joined', name => {
        console.log(name);
        users[socket.id] = name;
        socket.broadcast.emit('user-joined', name);
    });

    // If someone sends a message, broadcast it to other people
    socket.on('send', message => {
        socket.broadcast.emit('receive', { message: message, name: users[socket.id] })
    });

    // If someone leaves the chat, let others know 
    socket.on('disconnect', message => {
        socket.broadcast.emit('left', users[socket.id]);
        delete users[socket.id];
    });
})

const server_port = process.env.YOUR_PORT || process.env.PORT || 8000;
http.listen(server_port, () => {
    console.log(`Server is running on..... http://localhost:${server_port}`);
});