server.js

var express = require('express');
var sockjs  = require('sockjs');
var http    = require('http');

// 1. Echo sockjs server
var sockjs_opts = {sockjs_url: "http://cdn.jsdelivr.net/sockjs/1.0.1/sockjs.min.js"};

var sockjs_echo = sockjs.createServer(sockjs_opts);
sockjs_echo.on('connection', function(conn) {
    conn.on('data', function(message) {
        conn.write(message);
    });
});

// 2. Express server
var app = express(); /* express.createServer will not work here */
var server = http.createServer(app);

sockjs_echo.installHandlers(server, {prefix:'/echo'});

console.log(' [*] Listening on 0.0.0.0:9999' );
server.listen(9999, '0.0.0.0');

app.get('/', function (req, res) {
    res.sendfile(__dirname + '/index.html');
});