fune/testing/web-platform/tests/XMLHttpRequest/access-control-recursive-failed-request.htm

<!DOCTYPE html>
<html>
  <head>
    <title>Recursively repeated CORS requests with failed preflights should never result in unexpected behavior</title>
    <script src="/resources/testharness.js"></script>
    <script src="/resources/testharnessreport.js"></script>
    <script src="/common/get-host-info.sub.js"></script>
  </head>
  <body>
    <script type="text/javascript">
let requestCount = 0;
const requestMax = 10;

async_test((test) => {
  function preflightRequest() {
    const xhr = new XMLHttpRequest;

    xhr.onload = test.unreached_func("Request succeeded unexpectedly.");

    xhr.onerror = test.step_func(() => {
      assert_equals(xhr.status, 0);
      if (++requestCount >= requestMax) {
        test.done();
        return;
      }
      preflightRequest();
    });

    xhr.open("GET", get_host_info().HTTP_REMOTE_ORIGIN +
        "/XMLHttpRequest/resources/access-control-basic-denied.py");
    xhr.send();
  }

  preflightRequest();
});
    </script>
  </body>
</html>