Using ServiceWorker in Chrome today

ServiceWorker is a background worker, it gives us a JavaScript context to add features such as push messaging, background sync, geofencing and network control. In terms of network control, it acts like a proxy server sitting on the client, you get to decide what to do on a request-by-request basis. You can use this to make stuff work faster, offline, or build new features. I'm biased, but I think ServiceWorker changes the scope of the web more than any feature since XHR.