Update: A previous version of this post stated the Service Worker API is available in all applications using WKWebView. At this time it is only available in Safari, applications that use SFSafariViewController, and web applications saved to your home screen. The Service Worker API exposes persistent background processing capabilities to web pages. Support is available in Safari Technology Preview
![Workers at Your Service](https://cdn-ak-scissors.b.st-hatena.com/image/square/f9ff3252f389f4a004bc9bac7c7989342e27e005/height=288;version=1;width=512/https%3A%2F%2Fwebkit.org%2Fwp-content%2Fuploads%2FScreen-Shot-2018-01-31-at-1.52.33-PM.png)