This document covers various aspects of JavaScript, including debugging, optimizing, local and offline storage, and server-side JavaScript with web sockets. It presents tools, frameworks, and best practices for debugging (like Firebug), automated testing (e.g., QUnit, Jasmine), performance optimization techniques, and the use of local storage and session storage. It also discusses server-side JavaScript with Node.js and how to implement real-time messaging using web sockets.

1. Javascript Everywhere
Online, Offline and on the Server
Pascal Rettig
http://www.cykod.com
@cykod

2. Topics
• Debugging Javascript
• Optimizing Javascript
• Local Storage
• Offline Storage
• Server side Javascript + Web Sockets
(Time permitting)

3. Debugging Javascript
Or, alert(“Can only take you so far”);

4. Firebug
http://getfirebug.com/

5. Other browsers
• Chrome and IE8 have similar tools to
Firebug built in.
• Tools -> Developer Tools in both

6. Firebug 101
• Inspecting
• Modifying
• Tracking resources

7. Firebug 102
Getting rid of alert(...)
• Firebug console
• console.log(...), console.warn(...),
console.error(...)
• execute javascript directly from the console
• Firebug needs to be open

8. Javascript Debugging
• Firebug step debugger
• Setting watches
• Setting breakpoints
• Setting conditional breakpoints

9. The best type of bug...

10. The best type of bug...
... is one that’s caught
for you.

11. Javascript is a
lax language
Your javascript code will only be as rigorous as you are.

12. Consider lint’ing
http://javascriptlint.com/
Command line tool by Matthias Miller built on the
work done by Douglas Crockford (“JS, the good parts”)

13. Automated Testing
Frameworks
QUnit - used in JQuery
Jasmine - Created by Pivotal Labs, Inspired by RSpec

14. QUnit
By John Resig, Founder of JQuery
http://docs.jquery.com/Qunit
test("a basic test example", function() {
ok( true, "this test is fine" );
var value = "hello";
equals( "hello", value, "We expect value to be hello" );
});
module("Module A");
test("first test within module", function() {
ok( true, "all pass" );
});

15. Jasmine
From Pivotal Labs, Successor to JsUnit,
inspired (partly) by RSpec
http://pivotal.github.com/jasmine/
describe('Calculator', function () {
var counter = 0
it('can add a number', function () {
counter = counter + 2; // counter was 0 before
expect(bar).toEqual(2);
});
it('can multiply a number', function () {
counter = counter * 5; // counter was 2 before
expect(bar).toEqual(10);
});
});

16. Optimizing
Profiling
Javascript Optimization
Network Optimization

17. We should forget about small
efficiencies, say about 97% of the time:
premature optimization is the root of
all evil.
- Donald Knuth

18. Javascript Profiling
with Firebug

19. Javascript Profiling
with Firebug
• Click “profile”

20. Javascript Profiling
with Firebug
• Click “profile”
• Wait

21. Javascript Profiling
with Firebug
• Click “profile”
• Wait
• Click “profile” again

22. Some questions...
• Best way to add elements to arrays?
• Best way to create lots of objects?
• How bad is concatenating onto a HTML
string?
• How much to globals hurt?

23. Arrays
http://jsperf.com/array-selection-methods/2
var arr = [] var arr = []
for (var i = 0; i < len; i++) { for (var i = 0; i < len; i++) {
arr.push(i) arr[arr.length] = i
} }
var arr = new Array(len) var arr = []
for (var i = 0; i < len; i++) { for (var i = 0; i < len; i++) {
arr[i] = i arr[i] = i
} }
var arr = []
var arr = []
for (i = 0; i < len; i
for (i = 0; i < len; i++) {
++) {
arr.push(i)
arr[i] = i
}
}

24. Object Creation
http://jsperf.com/object-initialization-patterns-test
var Obj1 = function() {} var Obj3 = function() {
Obj1.prototype.yay = function(x) {}; function yay(x) {};
Obj1.prototype.boo = function(y) {}; function boo(y) {};
return {
for (var i = 0; i < numObjects; i++) { yay: yay,
new Obj1(); boo: boo
} }
}
var Obj2 = function() {
this.yay = function(x) {}; for (var i = 0; i < numObjects; i++) {
this.boo = function(y) {}; new Obj3();
} }
for (var i = 0; i < numObjects; i++) {
new Obj2();
}

25. Double check your
intuition...
• http://jsperf.com
• http://jsfiddle.net/

26. Web Page
Performance Tuning

27. Speed up game launch
• Games are often asset loading bound
• Consider a CDN (S3/Cloudfront)
• 24bit vs 8bit files
• Sprite maps
• Async or Load on demand Javascript:
• http://requirejs.org/
• http://headjs.com

28. Taking Javascript Home
• Local Storage
• Offline storage

29. Local Storage
Store data on the client for later use.

30. Isn’t that just like
a cookie?

31. Isn’t that just like
a cookie?
Yes and no

32. Local Storage vs. Cookies
Sent Available
Size Number
Each on
Limit Limit
Request? Server?
Local
5-10MB N/A No No
Storage
Cookies 4K 20 Yes Yes

33. Local Storage works for:
• Firefox 3.5, Safari 4, IE8, Chrome 4+
• Saving game state between visits without a
server
• Storing larger pieces of data

34. Testing for Local
Storage
Testing directly (From Dive Into HTML5)
function supports_local_storage() {
try {
return 'localStorage' in window &&
window['localStorage'] !== null;
} catch(e){ return false; }
}
Using Modernizr
if (Modernizr.localstorage) {
// Local Storage available
}

35. Using Local Storage
// Add an item to local storage
try {
localStorage.setItem(identifierString, valueString);
localStorage.identifierString = valueString;
} catch(e) {
if (e == QUOTA_EXCEEDED_ERR) { /* Do something */ }
}
// Retrieve an item
localStorage.getItem(identifierString);
localStorage.identifierString;
// Remove an item
localStorage.removeItem(identifierString);
delete localStorage[identifierString];
// Clear the entire per-domain DB
localStorage.clear();

36. Strings only...
Probably want to create an API on top
of localStorage
Storage.prototype.setObject = function(key, value) {
this.setItem(key, JSON.stringify(value));
}
Storage.prototype.getObject = function(key) {
return JSON.parse(this.getItem(key));
}
http://hacks.mozilla.org/2009/06/localstorage/

37. Better yet, use a
library...
http://www.jstorage.info/
$.jStorage.set(key, value)
value = $.jStorage.get(key)
value = $.jStorage.get(key, "default value")
Requires a library like jQuery, Prototype
Backwards compatible with IE7

38. Other HTML5 Storage
Options
• sessionStorage
- same as localStorage but per tab
• Web SQL
- Provides SQLite compatible DB storage
- WebKit only - good for mobile sync

39. Offline Storage

40. Why?
• Make apps available offline (Duh!)
• Make mobile apps that sync when
networked
• Force browsers to keep assets available

41. The set-up
1. Add a manifest file to your HTML:
<html manifest="/cache.manifest">
2. Make sure your manifest is served with:
AddType text/cache-manifest .manifest
3. Create the manifest listing cached files:
CACHE MANIFEST
/style.css
/application.js
/images/image1.jpg
...
/images/imageN.jpg
4. Listen for events on window.applicationCache

42. The Events on
window.applicationCache
Event When
checking First event, checking for a manifest
noupdate Manifest hasn’t changed
downloading Downloading the update
progress Periodically while downloading
Everything downloading, application
cached cached
A new cached is available, use
updateready swapCache() to swap out
Something returned a 404, so cache
obsolete is being deleted
error Something, somewhere went wrong

43. But...
If you have a simple app that you just want to
be cacheable online, you don’t need to do
anything special

44. Gotcha’s
• Disable server caching while testing or
your will go insane
• Make sure to update your manifest file each
time you update a resource. e.g.
“revisionXX”
• Probably want to auto-generate your
manifest file from a script so you aren’t
missing files.

45. Javascript on the Server

46. Why?
• Leverage existing javascript codebase
• Async good support for realtime and
Websockets

47. Introducing Node.js
http://nodejs.org/
• Built on Embedded Google V8 Engine
• Check out nodejs.com for installation
• Single threaded async
• Lots of callbacks

48. Node Packages
• NPM - node package manager, sort of like
Rubygems for node
• As easy as “npm install socket.io”
• export NODE_PATH=/path/to/node/lib to
use in node

49. Simplest Example
var http = require('http');
http.createServer(function (req, res) {
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end('Hello Worldn');
}).listen(8124, "127.0.0.1");
console.log('Server running at http://127.0.0.1:8124/');

50. WebSockets: the
problem
• Want realtime messaging
• Not supported in older browsers
• Removed from FF4 for the time being

51. WebSockets:
a solution
http://socket.io/
•Supports native WebSockets
•Has a fallback for flash
•Handles it all for you

52. The Server
var http = require('http'),
io = require('socket.io'),
fs = require ('fs'),
server = http.createServer(function(req, res){
fs.readFile("client/index.html", "binary", function(err, file) {
res.writeHead(200, {'Content-Type': 'text/html'});
res.end(file);
});
});
server.listen(8080);
var socket = io.listen(server);
socket.on('connection', function(client){
var messages = 0;
console.log('New Client');
client.on('message', function(message){
console.log(message);
setTimeout(function() {
client.send("Pong" + messages++);
},500);
});
client.on('disconnect', function(){ console.log('Client disconnected'); });
});

53. The Client
<script src="http://127.0.0.1:8080/socket.io/socket.io.js"></script>
...
<body>
<div id='status'></div>
<script>
var socket = new io.Socket("127.0.0.1");
socket.on('connect', function(){
$('#status').html('Connected!');
socket.send("Ping");
});
socket.on('message', function(req){
$('#status').html("Received: " + req);
setTimeout(function() {
socket.send("Ping");
},500);
});
socket.on('disconnect', function(){
$("#status").html("Disconnected");
});
socket.connect();
</script>

54. Thanks!
Pascal Rettig
pascal@cykod.com