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Oﬄine Mode
Web Applications for Offline Use
@pleckey | http://pleckey.me

Who is this guy?
Patrick Leckey
Director of Engineering
In-Touch Insight Systems Inc.
http://www.intouchinsight.com

Offline Mode - Web Applications Offline

... you're not guaranteed to
have connectivity the whole
way ...

What we have now ...
LocalStorage
window.localStorage
ApplicationCache
window.applicationCache
Chrome: 4+, Firefox: 3.5+, Safari: 4+
Mobile Safari: 3.2+, Android Browser: 2.1+
IE: 10+

LocalStorage
simple
straightforward
rather limited
ApplicationCache
complex
confusing
powerful

LocalStorage
... it's basically a shelf ...
Put stuff on the shelf
Take stuff off the shelf
Can only hold so much stuff

LocalStorage
Similar to Cookies
... but not transmitted on each request
Send what you want, when you want!

LocalStorage
Key / Value pairs
Limited storage size
Same Origin Policy!
http://pleckey.me != https://www.pleckey.me

LocalStorage
5 MB limit
As JavaScript strings ...
1.2345678
4 byte float? 9 bytes of characters?
Nope!
18-byte UTF-16 string

LocalStorage
window.localStorage.getItem( 'foo' ); // null
window.localStorage.setItem( 'foo', 'bar' );
window.localStorage.getItem( 'foo' ); // "bar"
window.localStorage.length; // 1
JSON.stringify( window.localStorage ); // {"foo": "bar"}
window.localStorage.removeItem( 'foo' ); // does nothing if key doesn't exist
window.localStorage.clear(); // remove ALL items

LocalStorage
What happens when the shelf is full?
try {
window.localStorage.setItem( 'foo', really_big_thing );
} catch ( e /* DOMException */ ) {
if ( e.name == 'QuotaExceededError' )
// Chrome, Safari, IE
else if ( e.name == 'NS_ERROR_DOM_QUOTA_REACHED' )
// Firefox
}

LocalStorage
Good Ideas
application state
user information

Bad Ideas
base64-encoded images
postal code lookup database

ApplicationCache
... is basically a ... uh ... cache ...
Pre-cache resources
Access resources offline
Fallback to alternates for dynamic resources

ApplicationCache
No storage limit
Event-driven API
Cache is based on manifest URL

ApplicationCache
<html manifest="/cache.manifest">
mime type must be text/cache-manifest

cache.manifest
CACHE
NETWORK
FALLBACK

cache.manifest
CACHE
CACHE MANIFEST
# Version: 8cf54be2
CACHE:
/favicon.png
/logo.png
/site/page2.html
explicitly cached resources

cache.manifest
NETWORK
CACHE MANIFEST
# Version: 8cf54be2
CACHE:
/favicon.png
...
NETWORK:
*
resources that require the user to be online
usually just "*"

cache.manifest
FALLBACK
CACHE MANIFEST
# Version: 8cf54be2
CACHE:
/favicon.png
/static.html
NETWORK:
*
FALLBACK:
/dynamic.php /static.html
resource to load if requested resource not available offline

ApplicationCache
cached items are always served from the application cache
the application cache will not update unless the cache
manifest file content changes

ApplicationCache
CACHE MANIFEST
# Version: 8cf54be2
CACHE:
/script.js
NETWORK:
*
text content has to be changed

Pretty Simple, right?
... and you thought it'd be that easy ...

Oops #1
Non-cached resources don't exist.
Even when you're online.
NETWORK:
*

Oops #2
The application cache works with the browser cache.
Sort of.
Cache-Control: max-age=9999999999

Oops #3
Caching the cache manifest.
It'll never update.
Cache-Control: no-cache, no-store

Clearing the ApplicationCache
HTTP/1.0 410 Gone

ApplicationCache Events
window.applicationCache.addEventListener( ... );
/**
* 'checking' - browser is checking for an update (always first)
*
* 'cached' - fired after first download of a new cache manifest
*
* 'downloading' - new / updated resources found, browser is fetching
*
* 'error' - manifest returned 404 or a download failed
*
* 'noupdate' - cache manifest has not changed
*
* 'obsolete' - manifest returned 410, cache deleted
*
* 'progress' - X of Y manifest resources downloaded
*
* 'updateready' - all updates downloaded
*/

ApplicationCache API
window.applicationCache.addEventListener( 'updateready', function( e ) {
alert( 'New version downloaded. Application will now reload.' );
window.location.reload();
} );
window.applicationCache.update();

ApplicationCache API
window.applicationCache.addEventListener( 'updateready', function( e ) {
alert( 'New version downloaded. Application will now reload.' );
window.applicationCache.swapCache();
} );
window.applicationCache.update();

iframe is your friend

<html>
<script type="application/javascript">
store large lookup data in iframes

<html manifest="/cache.manifest">
<iframe src=/slideshow/offline-mode-web-applications-offline/33191740/"iframe_js.html" width="0" height="0" border ="0"/>
</html>
CACHE MANIFEST
# Version: 1
CACHE:
/iframe_js.html
NETWORK:
*
include lookup data in cache manifest
load via iframe (same origin)

// index.html console
> window.awesome_data
Object {con: "foo", bar: "baz"}
var appCache = window.applicationCache;
if ( appCache.status != appCache.status.CACHED ) {
// not cached yet, do an AJAX lookup
} else {
return window.awesome_data.con; // "foo"
}

Single Page Applications
pre-cache static resources (speed!)

Native(ish) Web App
<meta name="apple-mobile-web-app-capable" content="yes"/>
<meta name="mobile-web-app-capable" content="yes"/>
runs full screen
built-in software updates
queue data for submission later

What Else Can I Do With This?
Come work for us!
Software Developer
User Experience
Data Scientist

Thank you!
Questions?
@pleckey | http://pleckey.com

�ݺ�ߣ

Offline Mode - Web Applications Offline

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