Based on the Workbox Advanced Recipes

To test:

npm install
npm run start

Then open http://localhost:8000 in a browser tab. You should just see the number 0.

Edit index.html to replace the "0" in the body tag on line 2 with a "1", and edit index.html to change the first line v variable from "0" to "1". Back in your browser, refresh the page.

After refreshing, you should still see a 0 in the tab, but you should also see a button at the bottom left corner. When you click it, the page should refresh, and you should see a 1 in the tab.