demo · v138

Service Worker sees prefetched requests

In Chrome 138 the active Service Worker's fetch handler is now invoked for requests originated by Speculation Rules prefetch. Register the worker below, inject a prefetch, watch the worker log the request — with the new Sec-Purpose: prefetch hint visible.

checking support…
sw: not registered
/v138/ /v149/

register the worker, then hover or click a prefetch trigger

the code

// sw.js
self.addEventListener("fetch", (e) => {
  // 138+: also called for SpeculationRules prefetch requests.
  const purpose = e.request.headers.get("Sec-Purpose") || "(none)";
  // log purpose, e.request.url, e.request.mode etc.
});

see also