chromium/chrome/test/data/extensions/api_test/shared_worker/service_worker_controlled/service_worker.js

// Copyright 2018 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

let urlsSeen = [];

self.addEventListener('fetch', e => {
  urlsSeen.push(e.request.url);
});

self.addEventListener('message', e => {
  e.source.postMessage(urlsSeen);
  urlsSeen = [];
});