css/cssom-view/element-scroll-promises.html

<!DOCTYPE html>
<title>Element.scroll* methods returning promises</title>
<meta name="timeout" content="long">
<meta name="viewport" content="width=device-width,initial-scale=1">
<link rel="author" title="Mustaq Ahmed" href="mailto:mustaq@chromium.org">
<link rel="help" href="https://drafts.csswg.org/cssom-view/#extension-to-the-element-interface">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/dom/events/scrolling/scroll_support.js"></script>
<style>
  .filler { height: 5000px }

  #scroller {
    overflow: scroll;
    width: 100px;
    height: 100px;
  }
</style>
<div id="scroller">
  <div class="filler"></div>
  <div class="filler"></div>
</div>
<script>
  "use strict";

  const scroller = document.getElementById("scroller");
  const scroll_methods = ["scroll", "scrollTo", "scrollBy", "scrollIntoView"];

  function reset() {
    scroller.scrollTo({ top: 0 });
    assert_equals(scroller.scrollTop, 0, "Sanity check starting position");
  }

  promise_setup(async () => {
    await waitForCompositorReady();
  });

  for (const scroll_method of scroll_methods) {
    for (const behavior of ["auto", "instant", "smooth"]) {
      const test_label = `Element.${scroll_method}(${behavior})`;

      promise_test(async () => {
        let result = scroller[scroll_method]({ behavior: behavior });
        assert_true(result instanceof Promise);
        const result_value = await result;
        assert_equals(typeof result_value, "object");
        assert_equals(typeof result_value.interrupted, "boolean");
      }, `${test_label}: return type`);

      promise_test(async () => {
        reset();
        const offset = 5000;

        let promise = (scroll_method != "scrollIntoView") ?
              scroller[scroll_method]({ top: offset, behavior: behavior }) :
              scroller.lastElementChild.scrollIntoView({ behavior: behavior });

        if (behavior != "smooth") {
          assert_equals(scroller.scrollTop, offset, "Position before await");
        } else {
          assert_true(0 <= scroller.scrollTop && scroller.scrollTop < offset,
                "Position before await");
        }

        const result_value = await promise;
        assert_equals(scroller.scrollTop, offset, "Position after await");
        assert_equals(typeof result_value, "object");
        assert_equals(typeof result_value.interrupted, "boolean");
      }, `${test_label}: promise behavior`);
    }
  }
</script>