This is a ServiceWorker template to turn small github pages into offline ready app.
Whenever I make small tools & toys, I create github repo and make a demo page using github pages (like this one).
Often these "apps" are just an index.html file with all the nessesary CSS and JavaScript in it (or maybe 2-3 html/css/js files). I wanted to cache these files so that I can access my tools offline as well.
Make sure your github pages have HTTPS enforced, you can check Settings > GitHub Pages > Enforce HTTPS of your repository.