open-with-defer-script-during-initial-about-blank-load.html

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This WPT test may be referenced by the following Test IDs:
- /html/webappapis/dynamic-markup-insertion/opening-the-input-stream/open-with-defer-script-during-initial-about-blank-load.html - WPT Dashboard Interop Dashboard

<!doctype html>

<title>document.open() with a deferred script during the initial about:blank load event</title>

<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=2041104">

<script src="/resources/testharness.js"></script>

<script src="/resources/testharnessreport.js"></script>

<div id="log"></div>

<script>

async_test(t => {

  const iframe = document.createElement("iframe");

  iframe.src = "about:blank";

  // Ensure a single load event and no assertion failures

  let loadCount = 0;

  iframe.addEventListener("load", t.step_func(() => {

    loadCount++;

    assert_less_than_equal(loadCount, 1, "iframe load must not refire");

    const d = iframe.contentDocument;

    d.open();

    d.write('<script defer src="data:text/javascript,window.parent.postMessage(\'defer-ran\', \'*\')"><\/script>');

    d.close();

  }));

  // Wait for written script to run

  window.addEventListener("message", t.step_func_done(

    e => assert_equals(e.data, "defer-ran")

));

  document.body.append(iframe);

}, "document.open() with a deferred script during the initial about:blank load event must not crash or refire load");

</script>