Intro To Node.js

Intro to Node.js
Chris Cowan
Lead Engineer
http://www.plus3network.com

Node’s Goal is to provide an
easy way to build scalable
network programs.

Node.js is NOT another
web framework!

But you can create a web framework using NPM modules.

Node.js is…
Web Server
TCP Server
Awesome Robot Controller
Command Line Application
Proxy Server
Streaming Server
VoiceMail Server
Music Machine
Anything that has to deal with high I/O

Node.js is
Server Side JavaScript!

Why Node.js?
• Non Blocking I/O
• Based on Chrome’s V8 Engines (FAST!)
• 15,000+ Modules
• Active Community (IRC, Mailing
Lists, Twitter, Github)
• Mac, Linux and Windows (all first class citizens)
• One Language for Frontend and Backend
• JavaScript is the Language of the Web

Installing Node.js
Mac OS X
1. Go to http://nodejs.org and click install
2. Install the downloaded package

Windows
2. Install the downloaded package

Linux (and *nix variants)
2. Decompress source and… ./configure … make … make install
( for Ubuntu use Chris Lea’s PPA – ppa:chris-lea/node.js )

Hello World
Create hello-world.js
console.log(‘Hello World’);

On the command line run
node hello-world.js

You should see
Hello World

Basic HTTP Server
var http = require('http');

var server = http.createServer(function (req, res) {
res.writeHead(200);
res.end('Hello World');
});

server.listen(4000);

*Running this script my development box,
I can achieve 10,000+ requests per second
with 100 concurrent connections
without breaking a sweat

Some people use the
core http module to
build their web apps,
most use a framework
like Express
or Connect or Flatiron or Tako or Derby or Geddy or Mojito or …

Visit
http://expressjs.com/guide.html
for a detailed guide
on using Express

What is Non-Blocking I/O?
And why should I care?

Blocking I/
// Get User – 20ms
$query = 'SELECT * FROM users WHERE id = ?';
$users = query($query, array($id));
print_r($users);

// Get Activities – 100ms
$query = 'SELECT * FROM activities ORDER BY timestamp LIMIT 50';
$activities = query($query);
print_r($activities);

// Get Leader Board – 150ms
$query = 'SELECT count(points) as total, user_id FROM activities LIMIT 50';
$leader_board = query($query);

270ms = SUM(user, activities, leaderboard)

Non-Blocking I/
// Get User – 20ms
var query = 'SELECT * FROM users WHERE id = ?';
db.query(query, [userId], function (err, results) {
console.log(results);
});

// Get Activities – 100ms
var query = 'SELECT * FROM activities ORDER BY timestamp LIMIT 50';
db.query(query, function (err, results) {
});

// Get Leader Board – 150ms
var query = 'SELECT count(points) as total, user_id FROM activities LIMIT 50';
db.query(query, function (err, results) {
});

150ms = MAX(user, activities, leaderboard)

The most jarring thing
about Server Side JavaScript
is thinking in callbacks

The Node Callback Pattern
awesomeFunction(arg, function (err, data) {
if (err) {
// Handle Error
}
// Do something awesome with results.
});

• Error first then success… ALWAYS!
• Because this is the de-facto standard 99.99999% of the time
you will be able to guess how a Node library will work.

Callbacks are the Devil’s Work!
Don’t go down this rabbit hole…
var userQuery = 'SELECT * FROM users WHERE id = ?';
var activityQuery = 'SELECT * FROM activities ORDER BY timestamp LIMIT 50';
var leaderBoardQuery = 'SELECT count(points) as total, user_id FROM activities LIMIT 50';

db.query(userQuery, [id], function (userErr, userResults) {
db.query(activityQuery, function (activityErr, activityResults) {
db.query(leaderBoardQuery, function (leaderBoardErr, leaderBoardResults) {

// Do something here

});
});
});

One of the biggest mistakes is to get yourself in
to callback hell by nesting callbacks inside of
callbacks inside of more callbacks.

Avoiding Callback Hell
• Keep your code shallow
• Break up your code into small chunks
• Use a sequential library like async
• Visit http://callbackhell.com

Async to the rescue!
var async = require('async');
var db = require(’db');

function getUser (callback) {
var query = 'SELECT * FROM users WHERE id = ?';
db.query(query, [userId], callback);
}

function getActivities (callback) {
var query = 'SELECT * FROM activities ORDER BY timestamp LIMIT 50';
db.query(query, callback);
}

function getLeaderBoard (callback) {
var query = 'SELECT count(points) as total, user_id FROM activities LIMIT 50';
db.query(query, callback);
}

var tasks = [getUser, getActivities, getLeaderBoard];
async.parallel(tasks, function (err, results) {
var user = results[0][0];
var activities = results[1];
var leaderBoard = results[2];
});

Async provides several useful
patterns for asynchronous control
flow including:
parallel, series, waterfall, auto and
queue.
Visit
https://github.com/caolan/async
for a detailed guide on using the async module.

The Node Package Manager
otherwise know as… NPM

It’s how you harness the
awesomeness of the
Node.js community!

Using NPM
It’s standard practice to install modules locally for your current project.
Modules are installed in the ./node_modules in the current directory.

To Install a new module

npm install <module>

To find a module in the NPM repository

npm search <search string>

To list the modules (and their dependencies) in the current project

npm list

To see module details

npm info <module>

DON’T INSTALL
MODULES GLOBALLY!
Unless they are tools like node-dev, jake, express, minify-js
OR linked development modules but more on that later.

NPM is awesome sauce!

Visit
https://npmjs.org
for more details about NPM and to
browse the current NPM Repository

Creating your own modules
• Node.js uses CommonJS Modules
• require(‘./example’) will load either
example.js or example/index.js or the entry
point specified in package.json
• Run npm init to bootstrap your new module
• Try to stick to creating Pure JavaScript
modules if possible. It will give you less
headaches down the road.

Basic Module Example
Everything exposed via module.exports is available as an instance variable.

var currentCount = 0;

module.exports.incr = function () {
return ++currentCount;
};

Once you’ve created a module in counter.js you use it like this…
var counter = require(’./counter');
var count = counter.incr();

Keep this in mind… modules are loaded once and cached. So when
you load the module a second time in your app, require just
returns the cache copied. This lets you do interesting things…

Installing your module
• Run npm link in the module working directory
• Then run npm link <module> in the your project
folder to link it from the global module to your
local node_modules.

• OR you can create a private registry
(See https://npmjs.org/doc/registry.html)

• OR just link it by hand :P

My Favorite Modules
• request • jake
• async • hogan.js
• node-dev • connect
• underscore • moment
• express • mysql

Questions?
Contact me at chris@chriscowan.us

Intro To Node.js

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