The Core Progressive Web App checklist says that a PWA should provide a custom offline page. The Optimial Progressive Web App checklist says that a PWA should provide an offline experience where the PWA works the same offline as it does online (wherever network connectivity isn't strictly required).
Learn more in the What is network reliability and how do you measure it? post.
How the Lighthouse offline audit fails
In the Lighthouse report UI the full PWA badge is given when you pass all of the audits in all of the PWA subcategories (Fast and reliable, Installable, and PWA optimized).
How to make your PWA work offline
Workbox is the recommended approach for adding
service workers to websites because it automates a lot of
boilerplate, makes it easier to follow best practices, and
prevents subtle bugs that are common when using the low-level
ServiceWorker API directly.
- Add a service worker to your app.
- Use the service worker to cache files locally.
- When offline, use the service worker as a network proxy to return the locally cached version of the file.
Try it! Learn how to add a service worker to your app with the Working with service workers codelab.
- Source code for Current page does not respond with a 200 when offline audit
- What is network reliability and how do you measure it?
- Service Workers: an Introduction