position-sticky-top.html

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This WPT test may be referenced by the following Test IDs:
- /css/css-position/sticky/position-sticky-top.html - WPT Dashboard Interop Dashboard

<!DOCTYPE html>

<title>position:sticky elements should respect the top constraint</title>

<link rel="help" href="https://www.w3.org/TR/css-position-3/#sticky-pos" />

<meta name="assert" content="This test checks that position:sticky elements obey their top anchor after scrolling" />

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

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

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

<body></body>

<script>

test(() => {

  const elements = setupStickyTest('top', 50);

  elements.scroller.scrollTop = 100;

  const nonStickyTopY = elements.container.offsetTop +

      elements.filler.clientHeight;

  assert_equals(elements.sticky.offsetTop, nonStickyTopY);

}, 'before reaching the sticking point the sticky box should not be offset');

test(() => {

  const elements = setupStickyTest('top', 50);

  elements.scroller.scrollTop = 200;

  // This math cancels to sticky.offsetTop == (scroller.scrollTop + 50), but

  // for clarity the calculations are left explicit.

  const nonStickyTopY = elements.container.offsetTop +

      elements.filler.clientHeight;

  const targetTopY = elements.scroller.scrollTop + 50;

  const stickyOffset = targetTopY - nonStickyTopY;

  assert_equals(elements.sticky.offsetTop, nonStickyTopY + stickyOffset);

}, 'after reaching the sticking point the sticky box should be offset');

test(() => {

  const elements = setupStickyTest('top', 50);

  elements.scroller.scrollTop = 300;

  const maxOffsetInContainer = elements.container.offsetTop +

      elements.container.clientHeight - elements.sticky.clientHeight;

  assert_equals(elements.sticky.offsetTop, maxOffsetInContainer);

}, 'the sticky box should not be pushed outside its containing block');

</script>