Peter Lubbers - Pro HTML 5 Programming

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CHAPTER 10 ■ CREATING HTML5 OFFLINE WEB APPLICATIONS
window.applicationCache has an update() method. Calling update() requests that the browser
update the cache. This includes checking for a new version of the manifest file and downloading new
resources if necessary. If there is no cache or if the cache is obsolete, an error will be thrown.
Building an Application with HTML5 Offline Web Applications
In this example application, we will track a runner’s location while out on the trail (with intermittent or
no connectivity). For example, Peter goes running, and he will have his new HTML5 Geolocation–
enabled phone and HTML5 web browser with him, but there is not always a great signal out in the
woods around his house. He wants to use this application to track and record his location even when he
cannot use the Internet.
When offline, the Geolocation API should continue to work on devices with hardware geolocation
(such as GPS) but obviously not on devices that use IP geolocation. IP geolocation requires network
connectivity to map the client's IP address to coordinates. In addition, offline applications can always
access persistent storage on the local machine through APIs such as local storage or Web SQL Database.
Figure 10-2 shows the application in action.
Figure 10-2. The application in action
To run this application, you will need a web server serving these static resources. Remember that
the manifest file must be served with the content type text/cache-manifest. If your browser supports the
application cache, but the file is served with the incorrect content type, you will probably see a cache
error.
To run this application with complete functionality, you will need a server that can receive
geolocation data. The server-side complement to this example would presumably store, analyze, and
make available this data. It may or may not be served from the same origin as the static application.