chromium/src/third_party/blink/web_tests/http/tests/devtools/network/resources/fetch-parallel-worker.js

self.onmessage = (event) => {
    Promise.all(
        event.data.map(url => {
            return fetch(url).then((res) => res.text());
        }))
        .then(results => {
            self.postMessage(results);
        });
};