css/css-position/position-sticky-nested-bottom.html

<!DOCTYPE html>
<title>Nested bottom-constrained position:sticky elements should render correctly</title>

<link rel="help" href="https://www.w3.org/TR/css-position-3/#sticky-pos" />
<meta name="assert" content="This test checks that nested position:sticky elements with a bottom constraint render correctly" />

<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 = setupNestedStickyTest('bottom', 25, 35);
  elements.scroller.scrollTop = 300;
  const nonStickyTopY = elements.container.offsetTop +
      elements.filler.clientHeight;
  assert_equals(elements.sticky.offsetTop, nonStickyTopY);
  // The inner sticky should not be offset from the outer.
  const nonStickyInnerTopY = elements.sticky.clientHeight -
      elements.innerSticky.clientHeight;
  assert_equals(elements.innerSticky.offsetTop, nonStickyInnerTopY);
}, 'before reaching the sticking point, neither sticky box should be offset');

test(() => {
  const elements = setupNestedStickyTest('bottom', 25, 50);
  elements.scroller.scrollTop = 150;
  const nonStickyTopY = elements.container.offsetTop +
      elements.filler.clientHeight;
  assert_equals(elements.sticky.offsetTop, nonStickyTopY);
  assert_equals(elements.innerSticky.offsetTop, 35);
}, 'the inner sticky can stick before the outer one if necessary');

test(() => {
  const elements = setupNestedStickyTest('bottom', 25, 35);
  elements.scroller.scrollTop = 100;

  const nonStickyTopY = elements.container.offsetTop +
      elements.filler.clientHeight;
  const nonStickyBottomY = nonStickyTopY + elements.sticky.clientHeight;
  const targetBottomY = elements.scroller.clientHeight +
      elements.scroller.scrollTop - 25;
  const stickyOffset = nonStickyBottomY - targetBottomY;
  assert_equals(elements.sticky.offsetTop, nonStickyTopY - stickyOffset);

  // The inner sticky has similar math, but its offsetTop is relative to the
  // sticky element and in this test is (height - the difference between the
  // top values).
  assert_equals(elements.innerSticky.offsetTop, 40);
}, 'both sticky boxes can be stuck at the same time');

test(() => {
  const elements = setupNestedStickyTest('bottom', 25, 35);
  elements.scroller.scrollTop = 0;
  assert_equals(elements.sticky.offsetTop, elements.container.offsetTop);
  assert_equals(elements.innerSticky.offsetTop, 0);
}, 'neither sticky can escape their containing block');

test(() => {
  const elements = setupNestedStickyTest('bottom', 25, 500);
  elements.scroller.scrollTop = 200;
  // It doesn't matter how big the inner sticky offset is, it cannot escape its
  // containing block (the outer sticky).
  assert_equals(elements.innerSticky.offsetTop, 0);
}, 'the inner sticky cannot be pushed outside the outer sticky');
</script>