This feature has existed on various builds of Chrome/Chromium for some time now. But Google hasn’t been touting it, and it wasn’t really clear how it would be used and/or useful. Well today, it’s very clear. And again, very cool. Essentially, Chrome-based web apps are going to be able to be always open, but hidden in the background.
Why would anyone want to use a web app without seeing it? A couple reasons. First, this allows the browser to notify you in realtime of certain updates, like chat requests or new messages. Second, this may allow the browser to pre-render any page so when you do open it, it will load instantly.
Obviously, the trade-off is the memory hit you take by running an app in the background, but presumably these could be coded to have a minimal impact in terms of memory usage.
Essentially, this gives web apps a “push” notification functionality like Apple uses for the iPhone and iPad. It’s a bit different since that system uses Apple own servers to ping your phone and doesn’t require an app to be open at all, but the effect is the same. A user wouldn’t realize the app is open, but would still get alerts about it.
Of course, there’s a security risk there. But Google addresses that in this way:
To protect our users’ privacy, we’ve made this functionality available only to apps and extensions; regular websites will not be able to open background windows. Developers will also need to declare the “background” capability on their apps.
That’s important beyond the security issue. It could make installing web apps actually useful. Up until now, most of the apps in the Chrome Web Store are similar to the ones that already exist on the web. But with this system, you’d have to “install” an app to get this system working.
Update: And here’s an example app Google has made to show how this will work. This book, when installed, will periodically update in the background.