lib/jsdom/living/nodes/HTMLLinkElement-impl.js
function fetchAndProcess(el) {
  const href = el.getAttributeNS(null, "href");

  if (href === null || href === "") {
    return;
  }

  const url = parseURLToResultingURLRecord(href, el._ownerDocument);
  if (url === null) {
    return;
  }

  // TODO handle crossorigin="", nonce, integrity="", referrerpolicy=""

  const serialized = whatwgURL.serializeURL(url);

  fetchStylesheet(el, serialized);
}
function fetchAndProcess(el) {
  const href = el.getAttributeNS(null, "href");

  if (href === null || href === "") {
    return;
  }

  const url = parseURLToResultingURLRecord(href, el._ownerDocument);
  if (url === null) {
    return;
  }

  // TODO handle crossorigin="", nonce, integrity="", referrerpolicy=""

  const serialized = whatwgURL.serializeURL(url);

  fetchStylesheet(el, serialized);
}
https://html.spec.whatwg.org/multipage/semantics.html#default-fetch-and-process-the-linked-resource TODO: refactor into general link-fetching like the spec.