"Works Offline" should simulate a navigation request

The “works offline” audit currently performs the following:

const requestPage = function() {
  const oReq = new XMLHttpRequest();
  oReq.onload = oReq.onerror = e => {
    // __returnResults is injected by driver.evaluateAsync
    __returnResults(e.currentTarget.status);
  };
  oReq.open('GET', '');
  oReq.send();
};

Some service worker implementations (like the one sw-precache uses) have logic in place to detect whether the incoming fetch event is associated with a Request whose mode is set to 'navigate', and take specific action when that’s the case—like falling back to a cached Response representing the App Shell, allowing them to work offline.

I understand that using an XMLHttpRequest is much easier to script than properly triggering a navigation request, though. (Even if the code used fetch(), it’s not possible to construct a Request with mode set to 'navigate'.) Maybe there’s something that could be done with creating an <iframe> and checking whether that loads properly? Or else scripting a navigation to the same URL and then detecting if that is successful? Any thoughts on those approaches?

[paullewis]

@jeffposnick Do you fancy giving that PR a go?

[wardpeet]

i’m up for this one as well, no rush 😃 @jeffposnick