Im trying to implement a service worker with fetch event like this.

self.onfetch = event => {
  const req = event.request;
  if (req.method !== 'GET') return;
  const url = new URL(req.url);
  const dlmatch = DOWNLOAD_URL.exec(url.pathname);
  if (dlmatch) {
    event.respondWith(decryptStream(dlmatch[1]));
  } else if (cacheable(url.pathname)) {
    event.respondWith(cachedOrFetched(req));
  }
};

The fetch event works fine if I use fetch() or HttpClient but not when o using anchors. It Always bypass The service worker. Any suggestions?

const a = document.createElement('a');
        a.href = downloadUrl;
        document.body.appendChild(a);
        a.click();