Tech io nodejs_20130531_v0.6

Tech I/O
Node.js Server Side JavaScript
Ganesh Kondal
May 31, 2013

Agenda
Background
Overview & Introduction
Sample Code
• Event Model
• Non Blocking I/O
• Modules
Key Concepts
Applicability
In the Industry
2

• Quick collation of material from various allowed sources
– net, books & slides – to introduce the team to Node.JS
• To provide a glimpse of Node.JS
About
For
Folks who don’t know anything about Node.JS

Background
• Node.js runs on V8 Javascript Engine.
• V8 is Google’s open source engine; written in C++.
• Created by Ryan Dahl in 2009.
• Runs on Linux systems and Windows systems.
• Per Node.js
• IO is too costly
• Thread per connection is too memory intensive
!! (Apache creates one thread per connection)
4

Introduction
• Node.js is ‘server-side JavaScript’.
• High-performance network applications framework,
• Well optimized for high concurrent environments.
• Command line tool to execute nodeJS code.
• Written with 40% JS and 60% C++ code.
• Lightweight - Uses an event-driven, non-blocking I/O model.
• Event-loops / Non-blocking IO via JavaScript’s callbacks.
• Programs for Node.js are written in JavaScript [no DOM
implementation ]
• Everything inside Node.js runs in a single-thread.
• Yes!! Its single threaded. Below code will block the
server for a second.
• All but your code is multi-threaded !!! 
5

‘Hello Node.js’
• Type your JS code, open cmd/terminal and type
this:
‘node FILE_NAME.js’
• To execute the code
• ‘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’
6

Event Loops
7
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++ Thread pool
(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

Non Blocking I/O
• Traditional I/O
• Non-traditional, Non-blocking I/O
8
var result = db.query(“select name from student”);
computeStudentExamResult(result); //wait for
result!
informResults(); //execution is blocked!
db.query(“select name from student”,function
(result){
computeStudentExamResult(result); //wait for
result!
});
informResults(); //executes without any delay!

Few things with Node.js
• You can create an HTTP server and print ‘hello world’ on the
browser in just 4 lines of JavaScript.
• 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.
9

Servers… in 3 lines of code
10
• Create HTTP Server and print ‘Hello World’ :
• TCP server on port 9000 that echoes the
request:
var http = require('http');
http.createServer(function (req, res) {
res.writeHead(200,
{'Content-Type': 'text/plain'});
res.end('Hello Worldn'); })
.listen(5000, "127.0.0.1");
var net = require('net');
net.createServer(function (socket) {
socket.write("Echo serverrn");
socket.pipe(socket); })
.listen(9000,"127.0.0.1");

Node Modules
• 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 mod = 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.
11

Applicability
• 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.
• High productivity (as long as the developer
understands/thinks in terms of callbacks, async I/O)
• Node.js principle – IO is costly.
• http://blog.mixu.net/2011/02/01/understandin
g-the-node-js-event-loop/
12

Not Applicable For
13
• Computation intensive tasks on server side, as the
event-loops are CPU hungry.
• Still in beta – so be cautious !!
• Can’t guarantee backward compatibility. Not a 1.0
• No match for enterprise level application
frameworks like Spring(java), Django(python), etc.
• Not battle tested yet!!!

Node.js in the Industry
• LinkedIn :
• On the server side, our entire mobile software stack is
completely built in Node. One reason was scale. The
second is Node showed us huge performance gains.
• Clouds 9 IDE
• eBay :
http://www.ebaytechblog.com/2013/05/17/how-we-built-ebays-first-
node-js-application/
For more refer - http://nodejs.org/industry/
14

Tech io nodejs_20130531_v0.6

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