Currently, there is not possible to add service workers to a website.
"A service worker is a script that your browser runs in the background, separate from a web page, opening the door to features that don’t need a web page or user interaction. "
More info on Service Workers: Service worker overview - Chrome Developers
This is related to this thread: How to I add a JS file (service worker) to the root folder of website in Sitejet? - #3 by Natapol_Supmanu