Nodejs

● Description
● Introduction
● Some (Confusing) Theory
● 4 Examples
● A couple of weird diagrams
● 2 Pics showing unbelievable benchmarks
● Some stuff from Internet
● And Homer Simpson
Agenda

Description
● V8 is an open source JavaScript engine developed by Google. Its written
in C++ and is used in Google Chrome Browser.
● Node.js runs on V8.
● It was created by Ryan Dahl in 2009.
● Is still in Beta phase. Latest version is 0.6.11
● Is Open Source. It runs well on Linux systems, can also run on Windows
systems.
● If you have worked on EventMachine (Ruby) or Python’s Twisted or Perl’s
AnyEvent framework then following presentation is going to be very easy.

Introduction
● In simple words Node.js is ‘server-side JavaScript’.
● In not-so-simple words Node.js is a high-performance network
applications framework, well optimized for high concurrent environments.
● It’s a command line tool.
● In ‘Node.js’ , ‘.js’ doesn’t mean that its solely written JavaScript. It is 40%
JS and 60% C++.
● From the official site:
‘Node's goal is to provide an easy way to build scalable network programs’ -
(from nodejs.org!)

Introduction: Advanced (& Confusing)
● Node.js uses an event-driven, non-blocking I/O model, which makes it
lightweight. (from nodejs.org!)
● It makes use of event-loops via JavaScript’s callback functionality to
implement the non-blocking I/O.
● Programs for Node.js are written in JavaScript but not in the same
JavaScript we are use to. There is no DOM implementation provided by
Node.js, i.e. you can not do this:
var element = document.getElementById(“elementId”);
● Everything inside Node.js runs in a single-thread.

● Single Threaded :
Node use a single thread to run instead of other server like Apache HTTP who spawn a thread
per request, this approach result in avoiding CPU context switching and massive execution
stacks in memory. This is also the method used by nginx and other servers developed to counter
the C10K problem.
● Event Loop :
Written in C++ using the Marc Lehman’s libev library, the event loop use epoll or kqueue for
scalable event notification mechanism.
● Non blocking I/O :
Node avoid CPU time loss usually made by waiting for an input or an output response
(database, file system, web service, ...) thanks to the full-featured asynchronous I/O provided by
Marc Lehmann’s libeio library.
These characteristics allow Node to handle a large amount of traffic by handling as quickly as
possible a request to free the thread for the next one.
Node has a built-in support for most important protocols like TCP, DNS, and HTTP (the one
that we will focus on). The design goal of a Node application is that any function performing
an I/O must use a callback. That’s why there is no blocking methods provided in Node’s
API.

Example-1: Getting Started & Hello
World● Install/build Node.js.
● (Yes! Windows installer is available!)
● Open your favorite editor and start typing JavaScript.
● When you are done, open cmd/terminal and type this:
‘node YOUR_FILE.js’
● Here is a simple example, which prints ‘hello world’
var sys = require(“sys”);
setTimeout(function(){
sys.puts(“world”);},3000);
sys.puts(“hello”);
//it prints ‘hello’ first and waits for 3 seconds and
then prints ‘world’

Some Theory: Event-loops & Architecture
● Event-loops are the core of event-driven programming, almost all
the UI programs use event-loops to track the user event, for
example: Clicks, Ajax Requests etc.
Client
Event loop
(main thread)
C++
Threadpool
(worker
threads)
Clients send HTTP
requests
to Node.js server
An Event-loop is woken up by
OS,
passes request and response
objects
to the thread-pool
Long-running jobs
run
on worker threads
Response is sent
back to main
thread
via callback
Event loop
returns
result to client

Some Theory: Non-Blocking I/O
● Traditional I/O
var result = db.query(“select x from table_Y”);
doSomethingWith(result); //wait for result!
doSomethingWithOutResult(); //execution is blocked!
● Non-traditional, Non-blocking I/O
db.query(“select x from table_Y”,function (result){
doSomethingWith(result); //wait for result!
});
doSomethingWithOutResult(); //executes without any delay!

Node.js Server VS Multi Threaded Server

What can you do with Node.js ?
● You can create an HTTP server and print ‘hello world’ on the browser in just
4 lines of JavaScript. (Example included)
● You can create a TCP server similar to HTTP server, in just 4 lines of
JavaScript. (Example included)
● You can create a DNS server.
● You can create a Static File Server.
● You can create a Web Chat Application like GTalk in the browser.
● Node.js can also be used for creating online games, collaboration tools or
anything which sends updates to the user in real-time.

Example -2 &3 (HTTP Server & TCP
Server)
● Following code creates an HTTP Server and prints ‘Hello World’ on the browser:
// Load the http module to create an http server.
var http = require('http');
// Configure our HTTP server to respond with Hello World to all requests.
http.createServer(function (req, res) {
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end('Hello Worldn');
});
// Listen on port 5000, IP defaults to 127.0.0.1
server.listen(5000, "127.0.0.1");
How to Run A Http Example:
CMD ->Node Filename.js o/p-> Open Browser and type url
http://hostname:Portnumber For This Example http://127.0.0.1:5000

●Here is an example of a simple TCP server which listens on port 6000 and
echoes whatever you send it:
// Load the http module to create an tcp server.
var net = require('net');
// Configure our TCP server to respond with Echo Sever to all requests.
net.createServer(function (socket) {
socket.write("Echo serverrn");
socket.pipe(socket);
});
// Listen on port 6000, IP defaults to 127.0.0.1
net.listen(6000, "127.0.0.1");
How to Run A Tcp Example:
CMD ->Node Filename.js
o/p-> Open Browser and type url like --
http://hostname:Portnumber
http://127.0.0.1:5000

Node.js Ecosystem
● Node.js heavily relies on modules, in previous examples require keyword
loaded the http & net modules.
● Creating a module is easy, just put your JavaScript code in a separate js
file and include it in your code by using keyword require, like:
var modulex = require(‘./modulex’);
● Libraries in Node.js are called packages and they can be installed by
typing
npm install “package_name”; //package should be available in
npm registry @ nmpjs.org
● NPM (Node Package Manager) comes bundled with Node.js installation.

Example-4: Lets connect to a DB
(MongoDB)
● Install mongojs using npm, a mongoDB driver for Node.js
npm install mongojs
● Code to retrieve all the documents from a collection:
var db = require("mongojs")
.connect("localhost:27017/test", ['test']);
db.test.find({}, function(err, posts) {
if( err || !posts) console.log("No posts found");
else posts.forEach( function(post) {
console.log(post);
});
});

When to use Node.js?
● Node.js is good for creating streaming based real-time services, web chat
applications, static file servers etc.
● If you need high level concurrency and not worried about CPU-cycles.
● If you are great at writing JavaScript code because then you can use the
same language at both the places: server-side and client-side.
● More can be found at: http://stackoverflow.com/questions/5062614/how-
to-decide-when-to-use-nodejs

Some Node.js benchmarksTaken from: http://code.google.com/p/node-js-vs-
apache-php-benchmark/wiki/Tests
A benchmark between Apache+PHP and
node.js, shows the response time for 1000
concurrent connections making 10,000
requests each, for 5 tests.
Taken from:
http://nodejs.org/jsconf2010.pdf
The benchmark shows the
response time in milli-secs
for 4 evented servers.

When to not use Node.js
● When you are doing heavy and CPU intensive calculations on server side,
because event-loops are CPU hungry.
● Node.js API is still in beta, it keeps on changing a lot from one revision to
another and there is a very little backward compatibility. Most of the
packages are also unstable. Therefore is not yet production ready.
● Node.js is a no match for enterprise level application frameworks like
Spring(java), Django(python), Symfony(php) etc. Applications written on
such platforms are meant to be highly user interactive and involve
complex business logic.
● Read further on disadvantages of Node.js on Quora:
http://www.quora.com/What-are-the-disadvantages-of-using-Node-js

Appendix-1: Who is using Node.js in
production?
● Yahoo! : iPad App Livestand uses Yahoo! Manhattan framework which is
based on Node.js.
● LinkedIn : LinkedIn uses a combination of Node.js and MongoDB for its
mobile platform. iOS and Android apps are based on it.
● eBay : Uses Node.js along with ql.io to help application developers in
improving eBay’s end user experience.
● Dow Jones : The WSJ Social front-end is written completely in Node.js,
using Express.js, and many other modules.
● Complete list can be found at:
https://github.com/joyent/node/wiki/Projects,-Applications,-and-
Companies-Using-Node

Appendix-2: Resource to get started
● Watch this video at Youtube:
http://www.youtube.com/watch?v=jo_B4LTHi3I
● Read the free O’reilly Book ‘Up and Running with Node.js’ @
http://ofps.oreilly.com/titles/9781449398583/
● Visit www.nodejs.org for Info/News about Node.js
● Watch Node.js tutorials @ http://nodetuts.com/
● For Info on MongoDB: http://www.mongodb.org/display/DOCS/Home
● For anything else Google!

Appendix-3: Some Good Modules
● Express – to make things simpler e.g. syntax, DB connections.
● Jade – HTML template system
● Socket.IO – to create real-time apps
● Nodemon – to monitor Node.js and push change automatically
● CoffeeScript – for easier JavaScript development
● Find out more about some widely used Node.js modules at:
http://blog.nodejitsu.com/top-node-module-creators

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