NodeJS - Server Side JS

Node.js – Server Side JavaScript
GaneshKondal
June 13, 2014

Agenda
• Intent
• Node JS – Background & Overview
• JS Basics
• Pre-Cursors
• Installation, Setup, IDE & NPM
• JS Basics – callback, blocking & non-blocking I/O
• NodeJS –Modules, simple server
• Node JS Architecture
• Blocking vs. Non-Blocking I/O – Comparison
• Web Application with Express MVC
• Project – Code Structure
• App Development Sequence
• Code Parts – UI Template, Router, Database invocation
• Industry Adoption
• Applicability – Suited / Not Suited for
• Next Session – Topics

Intent
• To introduce listeners to the NodeJS platform; discuss the key aspect of non-
blocking I/O; run through a sample web app developed using Express framework
• An hour of glimpsing around NodeJS – Nothing else
Follow-up
Follow-up sessions will extend the sample application to work with files, show case a
socket I/O based file explorer and integrate with NoSQL databases like MongoDB

4
Node JS – Background
• Node.js runs on V8 Javascript Engine
• V8 is Google’s open source engine; written in C++ for Chrome
• Created by Ryan Dahl in 2009 and first published in 2011
• Runs on Linux and Windows
• Development and Maintenance of NodeJS is done by Joyent
• Written in C/C++ (80%) and JavaScript (20%) and it is open source.
Overview
• Node.js is ‘server-side JavaScript’; event-driven async I/O
• Well optimized for high concurrency, high performance and network applications
• Uses an event-driven, non-blocking I/O model.
• Non-blocking I/O happens via JavaScript’s callbacks.
• Programs for Node.js are written in JavaScript [not DOM manipulation like in jQuery]
• Node JS executes in a single threaded fashion

5
Pre-Cursors
• Installation
• From website or
• Homebrew (mac OS) or Synaptic (Ubuntu)
• IDE –
• JetBrains WebStorm 8.0.1 OR
• Sublime Text OR
• Eclipse with nodeclipse
• NPM
• Node Package Manager enables get third party modules
• Two modes
• Global - installs modules c:users356992appdata…
• Local – in the same directory under node_modules
• Works based on package.json in the root folder
• Comes packaged with Node installation
Open Source
Node Repository

6
JavaScript – Basics
s1
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• Functions in JavaScript are objects – first class citizens
• Essentially, you can pass a function as a variable to another function call
• Closure
Callbacks are – a
Functional
programming paradigm
Callbacks a.k.a Higher-
Order function
Only the function
definition is passed;
function is not
executed
A closure is an inner
function that has
access to the outer
(enclosing) function’s
variables—scope chain
• When callback is invoked, if there is a ‘this’ reference; it will be ‘undefined’
• Handling ‘this’ in a callback is via JS methods of ‘apply(..)’ or ‘call(..)’ OR
• Have the ‘this’ stored in a variable called ‘self’ and use it.

7
Event Driven Programming – Blocking, Non-Blocking I/O
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Traditional I/O
Non-blocking I/O
var result = db.query(“select x,y from tableXY”);
doSomethingWithResult(result); //waits for the result!
doSomethingWithoutResult(); //execution is un-necessarily blocked!
db.query(“select x, y from tableXY”,
function (result){
// gets called once the result is ready!
doSomethingWithResult(result);
});
doSomethingWithoutResult(); //executes without any delay!
Callback on db query
completion event

8
Fundamentals – Modules, Sample Code
• Modules
• Referenced by file path or file name
• No Global Scope in NodeJS
• Modules are loaded only once
• Libraries in node are packages/modules
Module 1 Module
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Global
Scope
Scripts
within a
module
context
• Sample – Web Server in 3 lines
Classic Browser Runtime
Node Runtime & Scope
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Loads the ‘http’ module
Function that handles the incoming
requests. Executed by the main
thread of node.

Multi-Threaded HTTP Server – Blocking I/O
• On heavy load – we see more threads that leads to more context switching which in turn leads to
more CPU / Memory usage
• Classic discussion on threads vs. events is in Benjamin Erb’s Thesis
[Strongloop, 2014]

Node JS Architecture – Non-Blocking I/O
• On heavy load – we see more threads that leads to more context switching which in turn leads to
more CPU / Memory usage
• Classic discussion on threads vs. events is in Benjamin Erb’s Thesis
[Strongloop, 2014]

Node JS – Event Loop
• Node is single-threaded
• Follows an event-driven
functional programming
model
• Errors in the main thread
kills the server
• POSIX thread switching is
not costly
Million concurrent connections
http://blog.caustik.com/2012/08/19/node-js-w1m-concurrent-connections/
[www.udemy.com, 2014]

Node JS – Event Loop
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
• Node is single-threaded
• Follows an event-driven
functional programming
model
• Errors in the main thread
kills the server
Million concurrent connections
http://blog.caustik.com/2012/08/19/node-js-w1m-concurrent-connections/

Java vs. NodeJS –Performance [ Return data with constant sleep]
Java Stack & Description
• Java servlet returns ‘hello world’ with a
200ms sleep [ simulating a 200ms DB call]
• Executed in Apache Tomcat 6.0, JDK 6
• Tomcat runs in a multi-threaded mode &
in a blocking mode
Node v 0.10
• Returns a ‘hello world’ equivalent string
with a 200ms timeout set in call
• Node JS ran in the (defacto) non-blocking
mode
Not a comparison between Java vs. Node –
rather a comparison of blocking and non-
blocking I/O

Node JS – Run Sample Web Application
• Use cases we will see
• Get the list of players from NoSQL (MongoDB)
• Add a player to the list
• STEP 1 – setup
• Install Node
• Install Express
• Install Expres – Genertor
• Generate a node express project
• Install MongoDB
• STEP 2 – Package.json edit to suit your needs
• STEP 3 – Install dependencies
• STEP 4 – Run
d:nodejs> npm install express
d:nodejs> npm install express-generator
d:nodejs> express playerlist
d:nodejsplayerlist> npm install
d:nodejsplayerlist> npm start

Node JS – Project Structure
Jade HTML Preprocessor
Express Engine
Mongo DB
Monk
Node.js Server
d:nodejs> npm install express
d:nodejs> npm install express-generator
d:nodejs> express playerlist
V
M
C
Public images, CSS and JS files
URI routing; view attachment
View templates using Jade.
Multiple other options exists – ejs, jade
Mongo DB Data files
• Jade – Template engine. Very short syntax to create a HTML
• Monk – Small layer that enables MongoDB a super-easy task within NodeJS

Node JS – Code Parts – MVC
1) Import necessary modules
2) Initialize Express
3) Configure the express app
a. Logger
b. Views
c. Template engine
d. Static images directory
e. …
4) Configure the router
5) Router = Controller
a. Connects the model, jade view
b. Enables navigation across the URIs

Node JS – UI Template
• Jade is a server side templating engine – like Thymeleaf, JSP, ASP
• Short syntax to create HTML

Node JS – Code Parts contd.
• Router
• Database
View: Jade template name
View Model: “Model of the view”
JSON object passed to the view
1
2
3
Load ‘Mongo’, ‘Monk’ necessary to
connect to MongoDB
Put the Mongo DB reference handle
to the global request object
db.get - Monk APIs to fetch
db.insert,db.find({},fn)
are some of the other relevant APIs

Node JS – Deployment
• Simplistic – Newbie mode
• node server.js
• Command line execution. No restart; or no monitoring
• Dies with the command shell closing
• Little better
• node server.js &
• Running as a background application in *nix
• Will last than the shell that started it
• Script that loops & restarts the server
• Still limited the lifeline of the script that starts
• Improvised shell
• Cron based monitoring
• Log attached
• Auto start enabled
• External port monitoring enabled for load balancing
While :
do
// node server.js
// sleep x seconds
done
// description
// author
// specify port, Ethernet card
// attach a cron job – for every minute
// start in sudo mode
// ensure a log file is rolled
// attached the init.d in linux

20
Industry Adoption
Paypal’s Account Overview via NodeJS
• Timeline & Inventory
• Built twice as fast as the Java Application
• 33% fewer lines of code – compared to the same functionality in
Java /Spring
• 40% fewer files
• Performance
• Double the requests vs. Java Application
• 35% decrease in the average response time
• Essentially, page loading is faster than the Java App
• Stack
• NodeJS – Server
• KrakenJS – Secure and scalable layer that extends Express, which
provides convention
• Dust – Asynchronous templates

21
Pros & Cons
Pros
• Fast – Execution speed
• Faster to market – development speed
• Less lines of code
• Great community
• Proven with high volume systems
• Most suited for networking, I/O intensive applications
Cons
• Writing event driven code is complex compared to
synchronous code
• Writing a large business logic centric system is cumbersome
• Callback hell
• Exception handling is not straight forward

22
Suitability
Suitable Scenarios
• Most suited for networking, I/O intensive applications
• Applications that need high concurrency / Queued concurrent inputs
• Streaming Applications – like Chat servers
• Proxy Service
• Real time applications
• Monitoring Dashboards
• like Brokerage Dashboard (Node JS + Socket IO)
• Application Monitoring
• REST APIs
Not Suited For
• Large business logic centric systems
• Heavy server side computation is required

Next Session
• File handlers, Streams
• Event Emitters
• Error, Exception Handling
• Socket.IO
• Build & Deploy – using Grunt
• JS CoE – Seed project for node

Reference
• Ryan Dhals original presentation in JS Conf
http://s3.amazonaws.com/four.livejournal/20091117/jsconf.pdf
• Expess framework
• http://expressjs.com/guide.htmld
• Node JS - www.nodejs.org
• Event Loop – www.udemy.com
• Strongloop – how nodejs is faster
http://strongloop.com/strongblog/node-js-is-faster-than-java/

Why Node JS is faster [ Return data with constant sleep]
• Asynchronous Non-blocking I/O is the
root cause
• Not just I/O alone – all of node js 50k
modules are written in an async fashion
• Debuggers, monitors, loggers,
• Cluster manager
• File operation
• Java NIO alone is not enough

NodeJS - Server Side JS

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