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Home Interviews Explain the difference between cache, network, and stale-while-revalidate caching strategies in SW. – MindStick
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1 Answers

ICSM Computer
ICSM Computer 13 Aug 2025
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1. Cache-First Strategy

“Serve from the cache if you can, fall back to the network if you must.”

How it works:

  • Service Worker looks in the cache.
  • If found → return cached version immediately.
  • If not found → fetch from the network, store in cache for next time.

Best for:

  • Assets that rarely change (images, fonts, libraries like Bootstrap or jQuery).
  • Offline-friendly resources.

Pros:

  • Fast (no network request if cached).
  • Works offline.

Cons:

  • May serve outdated content unless you have a manual update flow.

Example:

event.respondWith(
  caches.match(event.request).then(cachedResponse => {
    return cachedResponse || fetch(event.request);
  })
);

2. Network-First Strategy

“Always try the network first, fall back to the cache if offline.”

How it works:

  • Try fetching from the network.
  • If successful → return response and update cache.
  • If network fails (offline or timeout) → use cached version.

Best for:

  • Dynamic content (news feeds, social media, APIs).
  • Data that changes frequently.

Pros:

  • Always fresh when online.
  • Still works offline with cached backup.

Cons:

  • Slower if network latency is high.
  • No content if both cache and network fail.

Example:

event.respondWith(
  fetch(event.request)
    .then(response => {
      const clone = response.clone();
      caches.open('dynamic').then(cache => cache.put(event.request, clone));
      return response;
    })
    .catch(() => caches.match(event.request))
);

3. Stale-While-Revalidate Strategy

“Serve from cache immediately, but quietly update it in the background.”

How it works:

  • Check cache:
    • If found → return it instantly to the user.
    • Meanwhile, fetch from network in background.
    • When network returns → update cache so next request is fresh.

Best for:

  • Content that changes occasionally but must load instantly (blogs, avatars, CSS files with infrequent changes).

Pros:

  • Instant load from cache.
  • Updates happen automatically in the background.

Cons:

  • First view after a change might show old content.
  • Requires logic to notify user of updates if needed.

Example:

event.respondWith(
  caches.match(event.request).then(cachedResponse => {
    const fetchPromise = fetch(event.request).then(networkResponse => {
      caches.open('dynamic').then(cache => cache.put(event.request, networkResponse.clone()));
      return networkResponse;
    });
    return cachedResponse || fetchPromise;
  })
);

Quick Comparison Table

Strategy Priority Offline Ready Freshness Use Case
Cache-First Cache → Network Yes Might be old Static assets, fonts, images
Network-First Network → Cache Yes Fresh APIs, frequently changing data
Stale-While-Revalidate Cache + Background Update Yes Slightly stale Semi-static content, fast UX
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