NodeJS, WebSockets and the real-time web

Today our team held first presentation of the series “lancers|conf”.

The idea behind “lancers|conf” is to let each team member prepare presentation once per 2 weeks, share newest IT-related technologies, websites and ideas.

Each presentation should not exceed total 10-15 minutes, where 7 minutes are for presentation and the rest of time is for questions from other team members. Why exactly 7 minutes is important? Einstein said:

“If you can’t explain it simply, you don’t understand it well enough”

Today’s topic was “NodeJS, WebSockets and the real-time web”. In this post I’m going to describe shortly what NodeJS is, who is using it and what for. At the end I will show an example of simple real-time chat build on NodeJS with WebSockets.

In few words, NodeJS is a server side software system, where programs are written in JavaScript.

Main features:

Event-driven programming
Asynchronous IO
Easy scalability

But most of all – NodeJS is extremely fast.

Who is using?

The main purpose of using this technology is

Mobile application / websites
Real time application
Data delivery services
HTTP Gateways
Games

WebSockets

WebSocket is a technology which provide real-time communication between server and clients. To see it more clearly, let’s check the main difference between standard approach and WebSockets. As an example, let’s imagine a message exchanging service between users.

Standard HTTP

Each time user want to see new message from other users he/she must send a request to the server (reload page by F5). In result, number of requests growing very rapidly.

Standard HTTP + AJAX

In this case, client is sending requests (e.g. every 100 miliseconds) and waiting for response. This is also not efficient.

WebSockets

Client does not need to do anything. If new message appear, server is pushing it directly to the clients. In result, number of request is very low.

Code sample

To create a simple real time chat service like explained above, we need only few lines of code.

Server side (app.js)

// set up environment
var express = require('express'),
    socketIo = require('socket.io'),
    http = require('http'),
    app = express().use(express.bodyParser()),
    server = http.createServer(app);

// start server and open WebSocket
server = server.listen(3000);
var io = socketIo.listen(server);

// Client -> Client communication
io.sockets.on('connection', function(socket) {
    // server is listening to 'broadcast' event
    socket.on('broadcast', function(data) {
        console.log(data);
        // send event with data to all clients
        io.sockets.emit('broadcast', data);
    });
});

Client side (index.html)

var socket = io.connect('http://localhost:3000/');

// listen to 'broadcast' event
socket.on('broadcast', function (data) {
    console.log(data.message);
    // do something
});

// send 'broadcast' event with message
socket.emit('broadcast', { message: 'hoge' });

Pros and cons

Advanteges

Very easy to learn (JavaScript)
Easy to develop and deploy data delivery service
With NodeJS real-time communication (WebSockets, data streaming) become easy

Disadvantages

One size does not fit all – building e-commerce site on NodeJS is not a good idea

Links and sources

NodeJS official website
http://nodejs.org

NodeJS on Japanese Wikipedia
http://ja.wikipedia.org/wiki/Node.js

Google V8 Engine
http://ja.wikipedia.org/wiki/Google_V8_JavaScript_Engine