fullscreen/api/element-request-fullscreen-same-manual.html

<!DOCTYPE html>
<title>Element#requestFullscreen() on the current fullscreen element</title>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="../trusted-click.js"></script>
<div id="log"></div>
<div id="target"></div>
<script>
async_test(t => {
  var target = document.getElementById("target");

  document.onfullscreenchange = t.step_func(() => {
    assert_equals(document.fullscreenElement, target);

    // The next requestFullscreen() should fire no events due to "If element is
    // doc's fullscreen element, terminate these subsubsteps."
    document.onfullscreenchange = t.unreached_func("fullscreenchange event");

    trusted_click(t, () => {
      target.requestFullscreen();

      // Wait until after the next animation frame.
      requestAnimationFrame(t.step_func_done());
    }, target);
  });
  document.onfullscreenerror = t.unreached_func("fullscreenerror event");

  trusted_request(t, target);
});
</script>