reading-scroll-forces-anchoring.html

<!DOCTYPE html>
<link rel="help" href="https://drafts.csswg.org/css-scroll-anchoring-1/">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
body { height: 1000px }
div { height: 100px }
</style>
<div id="block1">abc</div>
<div id="block2">def</div>
<script>
  // This test verifies that reading window.scrollY forces any pending scroll
  // anchoring adjustment to occur before computing the return value.
  async_test((t) => {
    scrollTo(0, 150);
    requestAnimationFrame(() => {
      step_timeout(() => {
        // Queue scroll anchoring adjustment.
        document.querySelector("#block1").style.height = "200px";

        // Reading scrollY should force both the layout and the adjustment to
        // occur synchronously.
        var y = scrollY;

        assert_equals(y, 250);
        t.done();
      }, 0);
    });
  }, 'Reading scroll position forces scroll anchoring adjustment.');
</script>

chromium/third_party/blink/web_tests/external/wpt/css/css-scroll-anchoring/reading-scroll-forces-anchoring.html