after-scrollable-range-shrinkage-002.html

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This WPT test may be referenced by the following Test IDs:
- /css/css-scroll-anchoring/after-scrollable-range-shrinkage-002.html - WPT Dashboard Interop Dashboard

<!DOCTYPE html>

<html>

<meta name="viewport" content="width=device-width">

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

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

<link rel="author" title="Mozilla" href="https://mozilla.org">

<link rel="help" href="https://drafts.csswg.org/css-scroll-anchoring/">

<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1779404">

<div style="height: 500vh;"></div>

<div id="anchor" style="height: 10px; background-color: blue;"></div>

<div style="height: 200vh;"></div>

<script>

promise_test(async t => {

  assert_equals(window.scrollY, 0);

  let anchorRect = anchor.getBoundingClientRect();

  // Scroll to the anchor node.

  window.scrollBy(0, anchorRect.y);

  assert_equals(window.scrollY, anchorRect.y);

  await new Promise(resolve => requestAnimationFrame(resolve));

  await new Promise(resolve => t.step_timeout(resolve, 0));

  // Shrink the first element so that scroll anchoring happens.

  document.querySelectorAll("div")[0].style.height = "100vh";

  await new Promise(resolve => requestAnimationFrame(resolve));

  await new Promise(resolve => requestAnimationFrame(resolve));

  const scrollAnchorPosition = window.scrollY;

  // Scroll back to (0, 0) to calculate the expected scroll anchor element

  // position.

  window.scrollTo(0, 0);

  anchorRect = anchor.getBoundingClientRect();

  assert_equals(scrollAnchorPosition, anchorRect.y);

}, "Scroll anchoring properly works after scrollable range shrinkage");

</script>

</html>