Node js

Node js
with npm,
installing express js
@RohanChandane

Last updated on 13th Oct 2013

...

On windows machine,
- Setting up environment variable is built in inside nodejs
directory
- after installation, type nodevars to install environment variable.
nodevars.bat is a batch file responsible for setting it up

What is Node / Node js?
- Node is Command line tool
- Download it and install
- It runs javascript code by typing ‘node your-script-file.js’

- Hosted on V8 Javascript engine
- uses V8 as standalone engine to execute javascript.

- Server-side javascript
- Node provides JavaScript API to access network & file system.
- These JavaScript files runs on the server rather than on the client side
- We can also write a server, which can be a replacement for something like
the Apache web server

...
- Uses event-driven I/O (non-blocking I/O)
- is just a term that describes the normal asynchronous callback
mechanisms.
- In node.js you supply callback functions for all sorts of things, and your
function is called when the relevant event occurs.
- So that means, it works parallelly on different I/O operations.
- eg. Code for reading from a file & reading values from a database can be
executed one after another (since node js is single threaded), and it will wait for
data to receive from file & database.
Once it receives data, it will call callback function related to function call.

- One language
- to write server side and client side code
- No need to learn server side language like Java & PHP

Why Node
1. Efficiency
- Response time
= server-side script execution time + time taken for I/O operation

- Node reduces the response time to the duration it takes to execute
the slowest I/O query
- Its mainly because ‘Single threaded - Event loop’
- Also called Event driven computing Architecture

- There is a need for high performance web servers

...
2. JavaScript
- JavaScript is universal language for web
developers
- Its single threaded
- Its dynamic

3. Speed
- Up till now, JavaScript was related to
browser
- We used it for DOM manipulation
- and our favourite browser to execute
javascript, is Chrome

...
- Chrome uses V8 engine
underneath to execute js
- V8 is the fastest javascript
execution engine
- V8 was designed to run in
Chrome’s multi-process model

V8 engine

- V8 is intended to be used both in a browser
and as a standalone high-performance engine

Asynchronous callback mechanisms
4. callbacks are invoked

functions, which are initiating
- I/O operations
- writing to a socket
- making a database query
& not going to return the value
immediately

event loop

3. event occurs

1. registers callbacks

2. loop wait for events

There's a single thread, and a single event loop, that handles all IO in node.js

Writing Server-side js with Node
Now, lets see how to write a server in
JavaScript
- creating 'server.js'
var http = require("http");
http.createServer(function(request, response) {
response.writeHead(200, {"Content-Type": "text/plain"});
response.write("Hello World");
response.end();
}).listen(8888);

- executing it:
node server.js

Passing function as parameter
lets say
function execute(someFunction, value) {
someFunction(value);
}
execute(function(word){ console.log(word) }, "Hello");

can also be written
function say(word) {
console.log(word);
}
function execute(someFunction, value) {
someFunction(value);
}
execute(say, "Hello");

Understanding server.js
var http = require("http");
function onRequest(request, response) {
console.log("Callback invoked");
response.writeHead(200, {"Content-Type":
"text/plain"});
response.write("Hello World");
response.end();
}
1
2
http.createServer(onRequest).listen(8888);
console.log("Server started");

3

4
single thread

...
This ‘server.js’ program executes in following
order
1. registers callbacks

onRequest

2. loop wait for events

listen(8888)

3. event occurs

Browser requests - localhost:8888

4. callbacks are invoked

function onRequest() gets execute

Some Basic Core Modules
Node has several modules compiled into the binary. Defined in node's
source in the lib/ folder. To load use require('modules identifier')

- HTTP

how to use require('http')

- Net

how to use require('net')

- DNS

how to use require('dns')

- Events

how to use require('events')

- Utilities

how to use require('util')

- File System

how to use require('fs')

- Operating System

how to use require('os')

- Debugger

how to use debugger

Some Global object
Available in all modules

- Console

how to use console

- Process

how to use process

- Exports

how to use exports

- require

how to use require()

- setTimeout

how to use setTimeout()

- clearTimeout

how to use clearTimeout()

- setInterval

how to use setInterval()

- clearInterval

how to use clearInterval()

Core Modules: usage
Net require('net')
- Asynchronous network wrapper. It can create server & Client.
- Following example program creates server. It can be connected
using Telnet/Putty & responds to all user provided data.
var sys = require("sys"),
net = require("net");
var server = net.createServer(function(stream) {
stream.setEncoding("utf8");
stream.addListener("connect", function() {
stream.write("Client connectedn");
});
stream.addListener("data", function(data) {
stream.write("Received from client: " + data);
stream.write(data);
});
});
server.listen(8000, "localhost");

NPM: npmjs.org
Node Package Manager (NPM)
- Node modules largely written in JavaScript which runs on the server
(executed by the V8 engine) rather than on the client side.
- These modules are registered in npm registry at registry.npmjs.org
- To use these modules while developing application, npm helps in
- installing Node js packages / Modules / Programs
- & linking their dependencies

- npm is a command line utility program
- npm is bundled and installed automatically with Node version 0.6.3 and
above
- On windows, after setting up environment variables npm command can
be executed from any desired location to install node packages

NPM Commands
npm -l
- display full usage info
npm <command> -h
- display quick help on command
- eg npm install -h
npm faq
- commonly asked questions
npm ls
- displays all versions of available packages installed on system, their
dependencies, in tree structure

…
npm install <module name>
- to install new modules
- on windows, command prompt should be running with admin rights
npm install <module name> -g
- to install new modules globally
- on windows at location C:Users<user>AppDataRoamingnpm

...
npm update
- update all listed packages to their latest version (in given folder)
- install missing packages
- removes old versions of packages
npm update -g
- update all listed global packages
npm update <pkg>
- update specific package

Installing node module: express js
- express js
- Web application framework for node js
- Provides robust set of features to build single and multi page, &
hybrid web application

- installing express js on windows
- Start cmd with admin rights
- Make sure you have set up environment variable for node js
- Go to your project directory and type npm install express

...
- installing express as global package
- Previously we installed express for particular folder
- But usually we install it globally
- To install express globally, type npm install express -g

- On windows, this will install express in
C:Users<user>AppDataRoamingnpm
- express js is ready to use now

...
- Create a express project
- Inside project directory type express and enter
- This will create a project structure and will display created files,
what are dependencies and how to run project

- This is instructing to install dependencies by staying in same
directory and type npm install

...
- Run express server
- To run this newly created project, type node app

- Go to browser and type localhost:3000

And now you can start editing
code to make it the way you
want.

...
- While setting up project
- you can pass certain parameters to choose templating engine
and stylesheet engine

- for example, following command will create project with support
for ‘less’ stylesheet and ‘ejs’ templating
express -c less -e
Off course it need to install dependencies

References
http://en.wikipedia.org/wiki/V8_(JavaScript_engine)
http://stackoverflow.com/questions/6632606/where-does-node-js-fit-within-theweb-development-context
http://debuggable.com/posts/understanding-node-js:4bd98440-45e4-4a9a-8ef70f7ecbdd56cb
http://www.nodebeginner.org/
http://howtonode.org/
https://npmjs.org/
http://nodejs.org/
Book:
Node: Up & Running - Tom Hughes-Croucher & Mike Wilson (O’reilly)

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