css/css-values/attr-invalidation.html

<!DOCTYPE html>
<title>CSS Values and Units Test: attr() invalidation</title>
<meta name="assert" content="Test attr() invalidation">
<link rel="help" href="https://drafts.csswg.org/css-values/#attr-notation">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
  div {
    width: attr(data-foo type(<length>));
  }
</style>

<html>
  <body>
    <div id="div" data-foo="10px"></div>
  </body>
</html>

<script>
  setup({ single_test: true });
  let elem = document.getElementById("div");
  let old_width = window.getComputedStyle(elem).getPropertyValue("width");
  elem.setAttribute("data-foo", "30px");
  let new_width = window.getComputedStyle(elem).getPropertyValue("width");
  assert_not_equals(new_width, old_width);
  done();
</script>