index.js

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

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

app.get('/', function(req, res) {
    //res.render(__dirname + '/views/index.ejs');
    res.sendFile(__dirname + '/index.html');
});

io.sockets.on('connection', function(socket) {
    socket.on('username', function(username) {
        console.log("User " + username + " connected.");
        socket.username = username;
        io.emit('is_online', '🔵 <i>' + socket.username + ' join the chat..</i>');
    });

    socket.on('disconnect', function(username) {
        console.log("User " + socket.username + " disconnected.");
        io.emit('is_online', '🔴 <i>' + socket.username + ' left the chat..</i>');
    })

    socket.on('chat_message', function(message) {
        io.emit('chat_message', '<strong>' + socket.username + '</strong>: ' + message);
    });

});

http.listen(3000, function() {
    console.log('listening on *:3000');
});