Skip to content

Instantly share code, notes, and snippets.

Last active August 18, 2023 09:15
  • Star 83 You must be signed in to star a gist
  • Fork 4 You must be signed in to fork a gist
Star You must be signed in to star a gist
Save adactio/3717b7da007a9363ddf21f584aae34af to your computer and use it in GitHub Desktop.
An attempt at a minimal viable service worker.
// Licensed under a CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
// HTML files: try the network first, then the cache.
// Other files: try the cache first, then the network.
// Both: cache a fresh version if possible.
// (beware: the cache will grow and grow; there's no cleanup)
const cacheName = 'files';
addEventListener('fetch', fetchEvent => {
const request = fetchEvent.request;
if (request.method !== 'GET') {
fetchEvent.respondWith(async function() {
const fetchPromise = fetch(request);
fetchEvent.waitUntil(async function() {
const responseFromFetch = await fetchPromise;
const responseCopy = responseFromFetch.clone();
const myCache = await;
return myCache.put(request, responseCopy);
if (request.headers.get('Accept').includes('text/html')) {
try {
return await fetchPromise;
catch(error) {
return caches.match(request);
} else {
const responseFromCache = await caches.match(request);
return responseFromCache || fetchPromise;
Copy link

dracos commented Dec 18, 2019

Just to note that the main gist here is missing an await in the "return fetchPromise" line (as given in @jakearchibald's update), which means as-is it won't respond from the cache for HTML pages - as the promise can always be returned so will be, regardless of whether it resolves or rejects.

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment