JavaScript: How to detect that the Internet connection is offline?

How to detect that the Internet connection is offline in JavaScript?

Facebook offline access step-by-step

UPDATE : Facebook offline_access permission is being deprecated. Please refer to the official documentation for more information.

Can you store JavaScript and CSS files in localStorage to improve the performance of an online web app?

I'm working on a web application, which acts pretty much like a native application for both iOS and Android. However the Javascript files (jQuery + my own) and the css file together are pretty large for mobile use, which make the app slow to load if the user doesn't have 3G enabled.

Android: Speech Recognition without using google server

I want to develop an Speech recognizer in android, which should work in offline. As the android's built-in speech recognizer uses google server which needs internet, i want an alternative which works in the absence of internet.