Can service workers cache POST requests?

Question

I tried to cache a POST request in a service worker on fetch event.

I used cache.put(event.request, response), but the returned promise was rejected with TypeError: Invalid request method POST..

When I tried to hit the same POST API, caches.match(event.request) was giving me undefined.

But when I did the same for GET methods, it worked: caches.match(event.request) for a GET request was giving me a response.

Can service workers cache POST requests? In case they can't, what approach can we use to make apps truly offline?

Answer 1

You can't cache POST requests using the Cache API. See https://w3c.github.io/ServiceWorker/#cache-put (point 4).

There's a related discussion in the spec repository: https://github.com/slightlyoff/ServiceWorker/issues/693

An interesting solution is the one presented in the ServiceWorker Cookbook: https://serviceworke.rs/request-deferrer.html Basically, the solution serializes requests to IndexedDB.