pointerevents/pointerevent_touch-action-modified_touch.html

<!doctype html>
<title>Deleting touch-action:none after pointerdown has no effect</title>
<link rel="help" href="https://w3c.github.io/pointerevents/#determining-supported-direct-manipulation-behavior" />
<meta name="viewport" content="width=device-width">
<link rel="stylesheet" type="text/css" href="pointerevent_styles.css">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/resources/testdriver.js"></script>
<script src="/resources/testdriver-actions.js"></script>
<script src="/resources/testdriver-vendor.js"></script>
<script src="pointerevent_support.js"></script>
<style>
  #target {
    width: 100px;
    height: 150vh;
    background-color: lightgreen;
    user-select: none;
  }
  .touchActionNone {
    touch-action: none;
  }
</style>
<body>
  <h1>Deleting touch-action:none after pointerdown has no effect</h1>
  <div id="target" class="touchActionNone" draggable="false">
    An unscrollable element that becomes scrollable at pointerdown.
  </div>
</body>
<script>
  "use strict";
  let target = document.getElementById("target");
  let pointercancel_received = false;

  document.body.addEventListener("pointerdown",
      () => target.classList.remove("touchActionNone"));
  document.body.addEventListener("pointercancel",
      () => pointercancel_received = true);

  promise_test(async () => {
    let pointerup_event = getEvent("pointerup", document.body);

    await touchScrollInTarget(target, "down");
    await pointerup_event;

    // Sanity-check: the class has been removed.
    assert_false(target.classList.contains("touchActionNone"));
    assert_false(pointercancel_received,
        "a pointercancel event is unexpected");
  }, "No scrolling after deleting touch-action:none after pointerdown");
</script>