About Offline Web App

HTML5 defines a special cache, commonly called "appcache" or application cache, that allows you to instruct the browser to cache certain resources—like images, CSS, JS, and others in a way that makes them available to the application even if the user’s browser is offline.

The application cache can store your entire website offline: all the JavaScript, HTML, and CSS, as well as all your images and resources.

The application is automatically updated every time the user visits your page while online. If even one byte of data has changed in one of your files, the application cache will reload that file.

Browser support for offline web application
The Offline Web Applications spec is supported in:
Safari 4+
Chrome 5+
Firefox 3.5+
Opera 10.6+
iOS (Mobile Safari) 2.1+
Android 2.0+

It is currently unsupported in all versions of IE.

Test browser support for offline web application
To test if the browser supports application cache functionality, use the following feature-detect:
var appcache_support = !!window.applicationCache;