how to use Service Worker to cache cross domain resources if the response is 404?

Question

w3:

6.2 Cross-Origin Resources and CORS¶
Applications tend to cache items that come from a CDN or other origin. It is possible to request

Answer 1

Unfortunately, there's no way to detect it.

For security reasons, it's explicitly not allowed: https://github.com/whatwg/fetch/issues/14.