chromium/third_party/blink/web_tests/external/wpt/wasm/jsapi/functions/incumbent.html

<!DOCTYPE html>
<meta charset="utf-8">
<title>Incumbent settings object for host functions</title>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>

<!-- This is the entry page. -->

<iframe src="resources/incumbent-incumbent.html"></iframe>

<script>
setup({ explicit_done: true });

// postMessage should pick the incumbent page as its .source value to set on the MessageEvent, even
// inside host functions.
const expectedURL = (new URL("resources/incumbent-incumbent.html", location.href)).href;

let testId = 0;

window.onload = () => {
  const relevantWindow = frames[0].document.querySelector("#r").contentWindow;

  function setupTest(t) {
    ++testId;
    const thisTestId = testId;

    relevantWindow.addEventListener("messagereceived", t.step_func(e => {
      const [receivedTestId, receivedSourceURL] = e.detail;

      if (receivedTestId !== thisTestId) {
        return;
      }

      assert_equals(receivedSourceURL, expectedURL);
      t.done();
    }));

    return thisTestId;
  }

  async_test(t => {
    const thisTestId = setupTest(t);

    frames[0].runWindowPostMessageVeryIndirectly(thisTestId, "*");
  }, "Sanity check: this all works as expected synchronously");

  async_test(t => {
    const thisTestId = setupTest(t);
    frames[0].runWindowPostMessageVeryIndirectlyWithNoUserCode(thisTestId, "*");
  }, "Start function");

  done();
};
</script>