Offline web applications with HTML5

Web applications are preferred over desktop applications because they are available 24x7 and are accessible from anywhere in the network. A couple of years back, the term network implied wired-network but more recently, due to availability of high-speed wireless networks and handy mobile devices, the dependency over wired-network has diminished greatly. Via wireless connectivity, web applications are now accessible from literally anywhere. But there could be situations when internet connectivity may get lost. This loss of connectivity could be due to various reasons, like user is in transit or is switching between networks or is simply at a remote location where the wired/wireless network isn't available.

• Major drawback of a typical web application is that, the moment internet connectivity is lost; it can no longer be accessed or used. Most of the desktop applications do fairly well in this situation. They switch to disconnected or offline mode and ensure continuous user experience even during loss of network connectivity. Offline mode requires availability of local cache. Applications keep a copy of the online data and the data entered during the offline mode in application cache. Example of a desktop application supporting disconnected mode is e-mail client application. It caches e-mail folders and calendar appointments locally and allows browsing them in offline mode.

• Designing web application to support offline mode has been a challenge so far. Various architectural solutions exists which either requires setting trust relationship in browser or involves smart client installation. HTML5 recognized this architectural pain-point and elegantly provisioned for offline capability. Let's see how.

• Developing an offline web application has twofold issues. One, how to make web application/pages available in disconnected mode and two, how to cache large data?