nodejs intro part one

The Server-side JavaScript

Budhram GurungBy -

node.js

Created by Ryan Dahl in 2009

Background

node.js runs on V8. It is a set of bindings to the V8 JavaScript VM.

V8 is an open source JavaScript engine developed by Google. Its written in C++ and is used in Google Chrome Browser.

Latest version is v0.10.18

Is Open Source. It runs well on Linux/Unix systems, can also run on Windows systems.

Hello World!!!

file : hello_world.js

console.log('Hello World!!!');

How you can run?

...$ node hello_world.js

Ouput: Hello World!!!

Hurray!!!Crossed most difficult step.

In simple words: Node.js is ‘server-side JavaScript’. In ‘Node.js’ , ‘.js’ doesn’t mean that its solely written JavaScript. It is 40% JS and 60% C++.

A command line tool

A REPL (Read-Eval-Print-Loop)

Introduction

Let's code through REPL...

Module

Just a JavaScript file Need to use 'exports' object

to make variable, function reusable

Use 'module.exports' to export whole object

Demo

node_modules folders

var x_module = require(x);

if x is not : - native module like 'util', 'http' etc - does not begin with '/', './' or '../'

then, check '/node_modules' at parent directory If not found, check '/node_modules' of parent's parent directoryand continue until the root of the tree is reached.

If again not found, throw module not found error.

node_modules example

1) /home/ram/projects/node_modules/bar.js

2) /home/ram/node_modules/bar.js

3) /home/node_modules/bar.js

4) /node_modules/bar.js

File at '/home/ram/projects/foo.js' called require('bar.js'), then node would look in the following locations, in this order:

npm, short for Node Package Manager

command-line utility for interacting with node.js repository that helps in:

- package installation, - version management, and - dependency management.

Total modules so far: 41,566.

How to install any package/module: ...$ npm install backbone

Important

terms

before you know

node.js

Callback

A piece of executable code, that is

passed as an argument to other code

which is expected to execute at

some convenient time.

Example Code

setTimeout(function(){ console.log('World'); }, 1000);

console.log('Hello ');

Output:Hello

......waiting 1 sec.......... World

Blocking IO vs Non-Blocking IO

var result = db.query(“select x from table_Y”);doSomethingWith(result); //wait for result! doSomethingWithOutResult(); //execution is blocked!

Blocking IO

Non-blocking IO

db.query(“select x from table_Y”, function (result){ doSomethingWith(result); //wait for result!

});doSomethingWithOutResult(); // executes without

// any delay!

Event Loop

request

close

Event Queue

Events processed one at a time

CheckingFor

Events

close

connection

request

Known Events

Events in DOM

The DOM triggers Events.

You can listen for those events.

DOM click

submit

hover

events

When 'click' event is triggered.

$('p').on('click', function(){ .......... });

attach

Events in node.js

Many objects in Node emit events.

net.Sever

fs.readStream

request

data

EventsEventEmitter

Events in node.js

request: An instance of http.IncomingMessage

response: An instance of http.ServerResponse

net.Server requestemit

function(request, response){ ..... }

When 'request' event is emitted

Event

attach

EventEmitter

Custom EventEmitter Example

Code your properly properly.Event loop main hang or go infinite.

Check Demo

More on node.js

node.js uses an event-driven, non-blocking I/O model, which makes it lightweight. (from nodejs.org!)

Makes use of event-loops via JavaScript’s callback functionality to implement the non-blocking I/O.

Everything inside node.js runs in a single-thread.

Easily building fast, scalable network applications.

Focused on performance.

Can handle thousands of concurrent connections with

minimal overhead(CPU/ Memory) on a single process.

Allows one to script programs that do I/O in JavaScript.

More on node.js

Architecture

Runs JavaScript, but isn’tprimarily JavaScript

Node Execution Stack

event_loop()

Node Execution Stack

event_loop()

socket_readable(1)

Node Execution Stack

event_loop()

socket_readable(1)

http_parse(1)

Node Execution Stack

event_loop()

socket_readable(1)

http_parse(1)

loads('index.html')

Node sends a request to the thread pool to load 'index.html'.

The stack unwinds...

Node Execution Stack

event_loop()

socket_readable(1)

http_parse(1)

loads('index.html')

Node Execution Stack

event_loop()

socket_readable(1)

http_parse(1)

Node Execution Stack

event_loop()

socket_readable(1)

Node Execution Stack

event_loop()

The request is sent to the disk.

In the meantime, someone else connects to the server.

This time requesting an in-memory resource.

Node Execution Stack

event_loop()

Node Execution Stack

event_loop()

socket_readable(2)

Node Execution Stack

event_loop()

socket_readable(2)

http_parse(2)

Node Execution Stack

event_loop()

socket_readable(2)

http_parse(2)

http_respond(2)

Node Execution Stack

event_loop()

socket_readable(2)

http_parse(2)

Node Execution Stack

event_loop()

socket_readable(2)

Node Execution Stack

event_loop()

The process sits idle.

The first request is still hanging.

Eventually the disk responds.

Node Execution Stack

event_loop()

Node Execution Stack

event_loop()

file_uploaded()

Node Execution Stack

event_loop()

file_uploaded()

http_respond(1)

Node Execution Stack

event_loop()

file_uploaded()

Node Execution Stack

event_loop()

Installation

node.js official site: http://nodejs.org/download/

Url: https://github.com/joyent/node/wiki /Installing-Node.js-via-package-manager

sudo apt-get updatesudo apt-get install python-software-properties python g++ makesudo add-apt-repository ppa:chris-lea/node.jssudo apt-get updatesudo apt-get install nodejs=0.10.18-1chl1~precise1

On winodws, you can use node.js installer.

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

Who is using Node.js?