HTML5: The Missing Manual, 2nd Edition

Chapter 11. Running Offline

If you want to view a website, you need to connect to the Internet. Everybody knows that. 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 Kardashian 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, a useful offline web application can tolerate intermittent network disruptions.

This fact is particularly important for people using smartphones and tablets. To see the problem, try traveling through a long tunnel while using a web application on one of these devices. Odds are you’ll get a nasty error page, and you’ll have 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 ...