Introduction to node.js
End to end web development w/
javascript
Or Kaplan
kaplanor@gmail.com

What is node?
Taking JS Beyond the Browser
Node.js is a framework for building scalable
server-side applications and network
oriented programs with asynchronous
javascript.

External
modules
Node modules
(fs,tcp http)
Node internals
Google V8

Full JavaScript Stack
• meteor.com

Before we start
• JavaScript JavaScript JavaScript

Hello world example
setTimeout(function () {
console.log("world");
}, 2000);
console.log("hello");
setInterval(function () {
console.log("world");
}, 2000);
console.log("hello");

The non-blocking notion
• Single threaded
• Instead of waiting use events
• Never wait for IO (socket, disk etc.)
• JS is natural for building async programs
• For blocking operation the node internals
uses thread pool to wait for operations to
finish.

Traditional I/O
var data = file.read('file.txt');
process(data);

Traditional I/O
var data = file.read('file.txt');
ZzZzZZZzz…
process(data);
Why wasting those cycles?!

Non-Blocking I/O
file.read('file.txt', function (data) {
process(data);
return success;
});
DoWhateverYouWishMeanwhile();

Node Modules
The true force of node

NPM
• NPM is a package manager for node.js
– http://npmjs.org/

Express Package
• RESTful module for node webapps
• Supports cookies, sessions, caching etc.
• www.expressjs.com

Example of Express API
var Express = require('express'),
app = Express.createServer();
app.get('/users/(:user)/?', function (req, res) {
res.send('hello ' + req.params.user);
});
app.listen(process.env.PORT || process.argv[3] || 8080);

Comet Use Case
• Comet is a way for the client to get a real
time event from the server
• How would you implement?
– Polling – using AJAX to poll for events for
events
– Long Polling – Send HTTP requests in
chain, the response is delayed.
– Streaming – Keep open socket to the server.

Requirements
• Comet servers need to maintain many
open connections
• Holding one thread per connection is
unacceptable
• Node.js approach is better – easier to
scale, less resources per connection.

Implementing using web sockets
• Introduced on HTML5
• Creating a thin layer over TCP/IP accepting
constrain of the web
• Supported by node.js
• On this Demo we will use the socket.io
module, which is HTML4 compatible web
socket

Chat Demo
Chat server in less than 40 lines of code
https://gist.github.com/4542595

Buffering vs. Streaming

Exec – buffering (callback)
var util = require('util'),
exec = require('child_process').exec,
child;
child = exec('cat *.js bad_file | wc -l',
function (error, stdout, stderr) {
console.log('stdout: ' + stdout);
console.log('stderr: ' + stderr);
if (error !== null) {
console.log('exec error: ' + error);
}
});

Spawn - streaming
var util = require('util'),
spawn = require('child_process').spawn,
ls = spawn('ls', ['-lh', '/usr']);
ls.stdout.on('data', function (data) {
console.log('stdout: ' + data);
});
ls.stderr.on('data', function (data) {
console.log('stderr: ' + data);
});
ls.on('exit', function (code) {
console.log('child process exited with code ' + code)
;
});

Live Site Tips
• Test your code
• Run static analysis
• Monitor your app
• Let it scale
• Continuous deployment
• Use process manager- SMF, forever or upstart
• Document your code
• Share code between client and server
• Explore the community
• Global uncaught exception handler
• Chaos monkey

Why should one use node.js
• You already code your client using JS
• Great Performance- http://four.livejournal.com/1019177.html
• Can support thousands of concurrent connections
• Easy to scale
• Ideal for the mobile era
• Fast development
• Easy debug
• No locks - V8 uses only one thread!
• Community

Good For
• Small-Medium projects
• Prototyping
• Fast scale servers
• Flexible dynamic application (inject code)
• Web sockets

Limitations
• New programming style
• Using only one thread
• Immature environment
• Limited stack trace
• A bug may crash the whole server – use
forever watch dog.
• Dynamic language – what’s your religion?

Some Patterns
• Always return values on last statement
• Pass callbacks
• Code is not linear avoid infinite
indentation (extract callback into named
functions)
• Promises
• Test using node unit – high coverage is
crucial

Debugging (V8)
• Builtin debugger-
http://nodejs.org/docs/v0.5.9/api/debugger.html
• Ndb - https://github.com/smtlaissezfaire/ndb
• Inspector – web based (webkit) debugger -
https://github.com/dannycoates/node-inspector
• Web storm - http://www.jetbrains.com/webstorm/
• Eclipse -
https://github.com/joyent/node/wiki/Using-
Eclipse-as-Node-Applications-Debugger

CoffeeScript
• A ruby like scripting language that compiles to JavaScript.
• Quick guide - http://jashkenas.github.com/coffee-script/
• Great slides at http://bodil.github.com/coffeescript/

References
• Node.js – http://www.nodejs.org
• Comet - http://amix.dk/blog/post/19577
• Comet - http://www.slideshare.net/amix3k/comet-with-nodejs-and-v8
• WebSockets - http://howtonode.org/websockets-socketio
• Best Practices - http://stella.laurenzo.org/2011/03/bulletproof-node-js-
coding/
• Best Practices - http://howtonode.org
• Node modules - https://github.com/joyent/node/wiki/modules
• Node on Production - http://dshaw.github.com/2012-05-jsday/#/16

Questions?
Or Kaplan
kaplanor@gmail.com