How do you debug a service worker?

A service worker moves through four stages: install (fired once when the browser first downloads a new or changed worker), waiting (if an old version still controls open tabs), activate (once it takes control, typically after all old tabs close or skipWaiting() is called) and idle, where the browser terminates it between events to save memory.

PWAs can work offline, but only for content their service worker has explicitly cached. Registering a service worker does not automatically make a site offline-capable — you decide what to cache (app shell, API responses, images) and what strategy to use (cache-first, network-first, stale-while-revalidate).

The Cache Storage API is a browser-native key-value store for Request/Response object pairs, accessible from both a service worker and the page via the global caches object. It is the primary mechanism PWAs use to store network responses — HTML, CSS, JS, images, API JSON — so they can be served offline or instantly on repeat visits.

localStorage is a simple synchronous key-value store limited to strings and roughly 5-10MB, and it is not accessible from inside a service worker. IndexedDB is an asynchronous, transactional database that can store structured objects, blobs and much larger amounts of data, and it is accessible from both the page and the service worker — making it the right choice for most PWA data storage.

Yes. The Screen Orientation API’s screen.orientation.lock("landscape") method (or "portrait") can force a specific orientation, but on most browsers it only works while the page is in fullscreen mode via the Fullscreen API. An installed PWA can also declare a preferred orientation directly in its manifest with the "orientation" field, which locks orientation for the whole standalone app.