transform-change.html

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This test has a WPT meta file that expects 1 subtest issues.
This WPT test may be referenced by the following Test IDs:
- /layout-instability/transform-change.html - WPT Dashboard Interop Dashboard

<!DOCTYPE html>

<title>Layout Instability: no layout shift for transform change</title>

<link rel="help" href="https://wicg.github.io/layout-instability/" />

<style>

body { margin: 0; }

#transformed { position: relative; transform: translateX(20px); width: 100px; height: 100px; background: blue; }

#child { width: 400px; height: 400px; }

</style>

<div id="transformed">

  <div id="child"></div>

</div>

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

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

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

<script>

promise_test(async () => {

  const watcher = new ScoreWatcher;

  // Wait for the initial render to complete.

  await waitForAnimationFrames(2);

  // Modify the transform, for which no shift should be reported.

  document.querySelector("#transformed").style = "transform: translateY(100px)";

  // Change size of child, for which no shift should be reported, either.

  document.querySelector("#child").style = "width: 300px";

  await waitForAnimationFrames(2);

  // No shift should be reported.

  assert_equals(watcher.score, 0);

}, 'no layout shift for transform change');

</script>