https://src-yqbqdyglpz.now.sh/
This was created for a talk about PWAs at Founders & Coders. This repo is both the slides and an example of a simple PWA. You can view the app/slides at the live URL above, or pull this repo and serve it with npx serve src.
The service worker code especially is extensively commented to hopefully explain what is happening every step of the way.
index.html contains the code that installs the service worker. From there the code in serviceworker.js takes over. manifest.json contains the configuration telling browsers how to display our PWA.