The trouble is trailing slashes and inconsistent behaviour between the service worker and the web server.

https://instantmultipageapp.com/images/ loads from the server, and not the service worker. Observe how it lacks the Blog link in the header, which is missing in what the server is rendering—see /images/index.html in the repository.

https://instantmultipageapp.com/images loads from the service worker, and the server serves /index.html for it (which is very wrong) rather than /images/index.html.

This is purely a bug in the demo. Kind of a fundamental bug that leaves me unimpressed, but a simple bug nonetheless. If you were to actually run the service worker on the backend, it’d resolve this kind of problem, and also the inconsistency between what the two platforms render, as seen in the missing Blog link.

This is just one bug you found. There are more edge cases for sure, serviceworkers intercepting requests and caching is a nightmare.

I think it’s better characterised in this way: service workers are dangerous because you can break things; so it’s very important that the foundations of your service worker are sound. If the foundations are sound (which takes effort), there’s nothing wrong with them. But ad hoc service workers, like this, are extremely dangerous.

Thanks for reporting. There were some problems on the backend but this has now all been solved.

Which in turn means that sites using this technique will not work in private browsing mode.

That is not correct. There were some issues on the backend but these have now been solved.