HEAD raping service worker

const cacheName = 'storage';

function signalTimeout(ms) {
  const controller = new AbortController();
  setTimeout(() => controller.abort(), ms);
  return controller.signal;
}

function log(msg) {
  console.log(msg);
}

self.addEventListener('fetch', e => {
  if(e.request.method != 'GET') return;

  e.respondWith(async function() {
    const url = new URL(e.request.url).pathname;
    const cache = await caches.match(e.request);

    if(cache) {
      try {
        const head = await fetch(url, {
          method: 'HEAD',
          signal: signalTimeout(7000)
        });
        const fetchedET = head.headers.get('last-modified');
        const cachedET = cache.headers.get('last-modified');
        if(fetchedET === cachedET) {
          log(`[${url}] Up to date, using cached`);
          return cache;
        }
      }
      catch(err) {
        const nw = err.name === 'AbortError' ? 'dogshit' : 'unavailable';
        log(`[${url}] Network is ${nw}, using cached`);
        return cache;
      }
    }

    try {
      const fetchedObject = await fetch(e.request);
      if(fetchedObject.ok) {
        const storage = await caches.open(cacheName);
        storage.put(e.request, fetchedObject.clone());
        log(`[${url}] New version, fetching and caching`);
      }
      return fetchedObject;
    }
    catch(err) {
      if(cache) return cache;
      throw err;
    }
  }());
});