Introduction to Node.js – What is Node.js? – Why Node.js?

What is Node.js?

Node.js is an event-driven I/O framework.

What is Node.js?

Node.js is an event-driven I/O framework.

Good at handling lots of different I/O connections at the same time.

What is Node.js?

Node.js is an event-driven server-side javascript I/O framework.

Good at handling lots of different I/O connections at the same time.

Achieves this by making all network I/O non-blocking and file I/O asynchronous

Node is not

• A web framework
• A programming language

Node is

• A tool for creating I/O based programs that need to be fast and/or handle lots of connections

Examples of I/O based programs:

• Databases (e.g. MySQL, PostgreSQL, MongoDB, Redis, CouchDB)
• APIs (e.g. Twitter, Facebook)
• HTTP/WebSocket connections (from users of a web app)
• Files (image resizer, video editor, internet radio)

Why Node.js?

• Asynchronous

• Asynchronous
• Non-blocking

• Asynchronous
• Non-blocking
• Javascript

Prototype-based programming

- Javascript has no classess

- Instead, function defines objects

function Person () {}
var p = new Person()							
						

Classless programming

What classes can do for us?

• Define local scope and namespaces
• Allow private attribute and methods
• Encapsulate code
• Organize applications in an object oriented way

Prototype-based programming

function Person (firstname, lastname) {
	this.firstname = firstname;
	this.lastname = lastname;
}

// Public method 'fullName'
Person.prototype.fullName = function() {
	return this.firstname + this.lastname;
}

var p = new Person('Juan', 'dela Cruz');
						

Anti-Patterns: Javascript Imports

• Spread code around files
• Link libraries
• No way to maintain private local scope/states/namespace
• Leads to: - Name collisions - Unnecessary access

Patterns: Modules

• An elegant way of encapsulating and reusing code
• Takes advantage of the anonymous closure features of Javascript
• Adopted by Node.js

Anatomy of a module

var ageLimit = 50; // private

module.exports = Person

function Person (firstname, lastname, age) {
	this.firstname = firstname;
	this.lastname = lastname;
	this.age = age;
}

Person.prototype.belowAgeLimit = function () {
	return this.age < ageLimit;
}							
						

Node modules

var http = require('http'),
  fs = require('fs'),
  mongoose = require('mongoose');
						

If you've programmed in Node, this looks familiar

Modules in the Wild

var express = require('express');
var fs = require('fs');
var io = require('socket.io');
var crypto = require('crypto');

var app	= express.createServer();
var staticDir = express.static;

io = io.listen(app);

var opts = {
  port: 1948,
  baseDir : __dirname + '/../../'
};

io.sockets.on('connection', function(socket) {
	socket.on('slidechanged', function(slideData) {
		if (typeof slideData.secret == 'undefined' || slideData.secret == null || slideData.secret === '') return;
		if (createHash(slideData.secret) === slideData.socketId) {
			slideData.secret = null;
			socket.broadcast.emit(slideData.socketId, slideData);
		};
	});
});

app.configure(function() {
	[ 'css', 'js', 'plugin', 'lib' ].forEach(function(dir) {
		app.use('/' + dir, staticDir(opts.baseDir + dir));
	});
});

app.get("/", function(req, res) {
	res.writeHead(200, {'Content-Type': 'text/html'});
	fs.createReadStream(opts.baseDir + '/index.html').pipe(res);
});

app.get("/token", function(req,res) {
	var ts = new Date().getTime();
	var rand = Math.floor(Math.random()*9999999);
	var secret = ts.toString() + rand.toString();
	res.send({secret: secret, socketId: createHash(secret)});
});

						

Asynchronous programming

• Node.js is entirely asynchronous

consider this analogy...

You go down to a fast food joint and order a cheeseburger, they will immediately take your order and then make you wait around until the cheeseburger is ready. In the meantime they can take other orders and start cooking cheeseburgers for other people. Imagine if you had to wait at the register for your cheeseburger, blocking all other people in line from ordering while they cooked your burger! This is called blocking I/O because all I/O (cooking cheeseburgers) happens one at a time. Node, on the other hand, is non-blocking, which means it can cook many cheeseburgers at once.

Asynchronous programming

• Node.js is entirely asynchronous
• You have to think differently

What's the output?

PHP

echo 'Hello';
sleep(2);
echo ' world.';							
						

Node.js

					
setTimeout(function () {
  console.log(' world.')
}, 2000)

console.log(' Hello');							
						

Asynchronous programming

• Node.js is entirely asynchronous
• You have to think differently
• Failure to understand the event loop and I/O based model could lead to anti-patterns (bad code)

consider this jQuery code...

$.post('/resource.json', function (data) {
	console.log(data)
});

Node.js simply extends this idea to I/O operations: when you start an operation like reading a file, you can pass control to back to Node and have your code run when the data has been read. For example:

// read the file /etc/passwd, and call console.log on the returned data
fs.readFile('/etc/passwd', function(err, data){
  console.log(data);
});

Core modules

Node has small group of modules (referred to as 'node core') presented to the public as API that you are intended to write programs with.

• fs - file system handling
• http, net, dgram - for working with network systems
• os - module for getting os information
• url, querystring, path - for parsing urls and paths
• dns - module for asynchronously resolving DNS queries

and a lot more...

Installation

Windows

Download pre-compiled binaries from http://nodejs.org/download

Linux / Unix

$ git clone https://github.com/joyent/node
$ cd node
$ configure 
$ make && make install

Ready for actual coding