Introduction to Node.js: What, why and how?

Introduction to Node.js:
What, why and how?
Christian Joudrey - @cjoudrey

“Node's goal is to provide an easy way to build
scalable network programs.”

What is node?

• Command line tool to run JavaScript:
$ node my_app.js

• Built on top of Google's V8 JavaScript engine

• Provides a JavaScript API for network and file system

• Event-based, non-blocking I/O APIs

my_app.js:

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

console.log('hello');

Running it:
$ node my_app.js
hello
world

The cost of I/O?

• Accessing RAM ~ 250 CPU cycles

• Disk operations ~ 41 000 000 CPU cycles
o Reading a file
o Writing to a file

• Network I/O ~ 240 000 000 CPU cycles
o Database query responses
o Http responses
o Memcache results

• I/O is expensive

• Most web applications are I/O bound, not CPU bound

Handling I/O

• Apache is multithreaded (depending on conf.)
o Spawns a thread per request (or process)

• Each request is in its own "box", blocking I/O is "okay".

result = query('SELECT * FROM ...');
print result.id;

Thread-per-connection is expensive

http://blog.webfaction.com/a-little-holiday-present

• nginx uses an event-loop, like node.

Enter node...

• Single thread for your code

• ...but, I/O runs in parallel

• Handle thousands of concurrent connections with a single
process

• Need to be very careful with CPU-intensive code

I/O in node

• No function should directly perform I/O.

• To receive info from disk, network, or another process there
must be a callback.

• Callbacks are typically in the format:
function (err, result) { }

query('SELECT * FROM ...', function (err, result){
if (!err) {
print result.id;
}
});

CommonJS Module System

mymodule.js:

module.exports.add = function (a, b) {
return a + b;
};

Using the module:

var mymodule = require('mymodule');
console.log(mymodule.add(5, 2));

Built-in Modules

• File System
require('fs');

• HTTP Client and Server
require('http');

• TCP Sockets
require('net');

• Many more: http://nodejs.org/docs/v0.4.8/api/

Getting Started

• Node.js: http://nodejs.org/#download

• Build instructions: http://bit.ly/egLfzu
Mac: brew update && brew install node
• npm, a package manager for Node:
curl http://npmjs.org/install.sh | sh

• Many modules at: http://search.npmjs.org/

• Windows support isn't great (for the moment)

Reading a JSON File
var fs = require('fs');
var file = __dirname + '/test.json';

fs.readFile(file, 'utf8', function (err, data) {
if (err) {
console.log('Error: ' + err);
return;
}

data = JSON.parse(data);

console.dir(data);
});

https://gist.github.com/988107

Simple HTTP Server

var http = require('http');

var s = http.createServer(function (req, res) {
var headers = {'Content-Type': 'text/html'};
req.writeHead(200, headers);
res.end('<h1>hello world</h1>');
});

s.listen(8080, '127.0.0.1');

https://gist.github.com/988108

Express makes HTTP easier

• Node's HTTP module is low level.

• Express is a simple framework inspired by Sinatra (Ruby).

• Installing Express:
npm install express && npm install jade

• Robust verb-based routing
o app.get('/about', function(req, res) { });
o app.post('/login', function(req, res) { });

• Templating (with Jade or EJS)

• Sessions

Getting Started with Express

• Generate skeleton apps:
express –help

• Generate app with sessions and template engine:
express --sessions --template jade hello/

• Generated structure:
$ ls hello/
app.js logs pids public test views

$ ls hello/views/
index.jade layout.jade

Useful Modules

• Express - Sinatra-like Web Framework
http://expressjs.com
npm install express

• Jade - HAML-like Template Engine
http://jade-lang.com
npm install jade

• Socket.IO - Cross-browser WebSocket library
http://socket.io/
npm install socket.io

Interesting Links

• Lots of Express examples: http://bit.ly/ExpressExamples

• Express Documentation: http://bit.ly/ExpressDocs

• NodeMTL.com Source Code: http://bit.ly/iZCjod

• Database wrappers and ORMs:
o Mongoose (MongoDB, ORM-like):
https://github.com/LearnBoost/mongoose
o Couch-ar (CouchDB, Active Record implementation):
https://github.com/scottburch/couch-ar

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