Code to find all opaque responses currently cached, and return their URLs.

find-opaque-responses.js

async function findOpaqueResponses() {
  const cacheNames = await caches.keys();
  const urlsResultingInAnOpaqueResponse = [];
  for (const cacheName of cacheNames) {
    const cache = await caches.open(cacheName);
    const requests = await cache.keys();
    for (const request of requests) {
      const response = await cache.match(request);
      if (response.status === 0) {
        urlsResultingInAnOpaqueResponse.push(request.url);
      }
    }
  }
  return urlsResultingInAnOpaqueResponse;
}