mozilla-release/testing/web-platform/tests/resource-timing/cross-origin-status-codes.html

<!doctype html>
<html>
<head>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src=/common/get-host-info.sub.js></script>
</head>
<body>
<img id="img_200">
<img id="img_307">
<img id="img_404">
<img id="img_502">
<script id="script_200"></script>
<script id="script_307"></script>
<script id="script_404"></script>
<script id="script_502"></script>
<script>
async_test(t => {
  let destUrl = get_host_info().HTTP_REMOTE_ORIGIN + '/resource-timing/resources/';
  let statusCodes = ['200', '307', '404', '502'];
  statusCodes.forEach(status => {
    document.getElementById('img_' + status).src = destUrl + 'status-code.py?status=' + status;
    document.getElementById('script_' + status).src = destUrl + 'status-code.py?status=' + status + '&script=1';
  });
  let nameMap = {};
  let firstEntry = null;
  // We will check that the non-timestamp values of the entry match for all entries.
  const keys = ['entryType', 'nextHopProtocol', 'transferSize', 'encodedBodySize', 'decodedBodySize'];
  new PerformanceObserver(t.step_func(entryList => {
    entryList.getEntries().forEach(entry => {
      if (!entry.name.includes("status-code"))
        return;

      nameMap[entry.name] = true;
      if (!firstEntry) {
        firstEntry = entry;
      } else {
        keys.forEach(key => {
          assert_equals(entry[key], firstEntry[key], `Discernible difference in ${key} for ${entry.name}`);
        });
      }
    });
    if (Object.keys(nameMap).length === 8) {
      t.done();
    }
  })).observe({entryTypes: ['resource']});
}, "Make sure cross origin resource fetch failures with different status codes are indistinguishable");
</script>