Service Workers & Progressive Web Apps

Which of the following is NOT a valid caching strategy for Service Workers?

self.addEventListener('fetch', event => {
  event.respondWith(
    caches.match(event.request)
      .then(response => {
        return response || fetch(event.request);
      })
  );
});

Cache First
Network First
Cache Only
Browser Default
Common caching strategies include: 1) Cache First - check cache before network, 2) Network First - try network, fall back to cache, 3) Cache Only - only serve from cache, 4) Network Only - always use network, 5) Stale While Revalidate - serve from cache while updating. 'Browser Default' isn't a valid strategy as Service Workers must explicitly define how to handle requests through the fetch event.

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