HTML5: The Missing Manual

Chapter 10. Offline Applications

If you want to view a website, you need to connect to the Internet. Everybody knows that by now. So why a chapter about offline applications? The very notion seems so last century. After all, didn’t web applications overthrow several generations of offline, desktop applications on their way to conquering the world? And there are plenty of tasks—from following the latest Charlie Sheen sightings to ordering a new office chair—that just wouldn’t be possible without a live, real-time connection. But remember, even web applications aren’t meant to stay permanently online. Instead, they’re designed to keep working during occasional periods of downtime when a computer loses its network connection. In other words, an offline web application tolerates intermittent network disruptions.

This fact is particularly important for people using web-enabled phones and tablets. To see the problem, try traveling through a long tunnel while working on a web application with one of these devices. Odds are you’ll get a nasty error page, and you’ll need to start all over again when you get to the other side. But do the same with an offline web application, and you’ll avoid interruption. Some of the features of the web application may become temporarily unavailable, but you won’t get booted out. (Of course, some tunnels are longer than others. An ambitious offline web application can keep working through a three-hour plane flight—or a three-week trip to the Congo, if that’s ...