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We’ve got a website for that
HTML5, offline and the future of the mobile web
Open Source Junction 3
Trinity College, Oxford 20-21 March 2012
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The web has transformed
our lives. Now we need
that stuff on the move.
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1999: WAP
. Seriously?
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2001: BlackBerry. Now we’re talking.
(except ironically we’re not talking because Blackberry wouldn’t add
phone capabilities for another 3 years)
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2007: iPhone. Cracked it.
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2008: Apps arrive. Web largely forgotten.
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But wait,
what exactly is an app, anyway?
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Adaptive interaction
Adaptive design
+
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But, couldn’t we just make a
website do all that app stuff?
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Challenges for the web
• Layout
– Adapt, adapt, adapt
• Navigation and interaction
– Interpreting touches is a subtle art
• Offline use
– Just reinvent the whole way the web works
• Rethink backend architecture
– Fewer pages, more APIs
• Analytics
– Record activity while user is offline
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Flowed columns
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Flowed columns
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So you want to use the Internet
when you’re not online?
Good luck with that.
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Breaking it down
• Launching the app offline
• Making text content available offline
• Storing content images offline
• Dealing with quota limits
• Analytics
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Offline technologies
Application cache (manifest)
WebSQL / SQLite / IndexedDB
Local storage
Cookies
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Launching
• Application cache
• Manifest is atomic – download all or none
– Boot page, fonts, sprites, splash screen, icons only.
• Webkit manifest bug – obscure naming of the
manifest helps
• Set dynamic comment in manifest for dev
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Manifest contents
• Fonts
• Sprites
• Icons
• Splash screen
• One HTML page
• JavaScript
• HTML
• CSS
YES
NO
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CACHE MANIFEST
# Version: 2012030613
/favicon.ico
/lib/imgs/sprite.png
/lib/imgs/splash-logo.jpg
/lib/fonts/main.ttf
FALLBACK:
/ /controller.html
NETWORK:
*
Cached files
Use network
when possible
Fallback for
booting offline
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Boot process
• Fallback page is loaded from app cache
• Load resources from local storage
– JS, CSS, HTML
• Use cookie to identify user
• Load requested content from local DB
• Display it
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Offline text content
• Client side database
• IndexedDB is coming, SQLite works now.
• 5MB for free, up to 50 with consent
• Use localStorage for index, as it's faster
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Offline images
• Lots. High turnover. Binary data.
• Client side database
• Download base64 encoded strings
• Render as data: URIs
– 
• Nice: Stops operators interfering
• Unfortunate: 30% bigger
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Quota
Native apps get whatever
storage they want
!
Web apps have
hard storage limits
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Tricks for super storage
• local storage and local DB use UTF-16 text
• That’s a minimum 2 bytes per character
• Pack ASCII into (pretend) UTF-16:
if (in.length % 2 !== 0) in += ' ';
for (i = 0, l = in.length; i < l; i+=2) {
out += String.fromCharCode(
(in.charCodeAt(i)*256) + string.charCodeAt(i+1)
);
}
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App cache, local storage, eval()ed JavaScript,
invalid UTF-16…
Congratulations, you’ve made a
debugging nightmare
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Useful tools
• Charles
– www.charlesproxy.com
• WeinRE
– phonegap.github.com/weinre/
• WebDriver for mobile browsers
– http://code.google.com/p/selenium/wiki/
WebDriverForMobileBrowsers
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In summary
• Ease of use is critical. Adapt, adapt, adapt.
• The web can do this
• Web approach retains all the benefits of the
web that you give up when building native.
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“Don’t build native apps,
build web apps”
-‐
Tim
Berners-‐Lee
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Questions?
• Andrew Betts
• [email protected]
• You should follow me on twitter here:
– @triblondon
• Build this stuff:
– assanka.net/jobs