| <!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> |
