resnap-on-overflowing-snap-area.html (1921B)
1 <!DOCTYPE html> 2 <meta name="viewport" content="width=device-width,initial-scale=1"> 3 <link rel="help" href="https://drafts.csswg.org/css-scroll-snap/#re-snap" /> 4 <link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1978946"> 5 <script src="/resources/testharness.js"></script> 6 <script src="/resources/testharnessreport.js"></script> 7 <style> 8 #scroller { 9 overflow-y: auto; 10 scroll-snap-type: y mandatory; 11 width: 100vw; 12 height: calc(100svh - 80px); 13 } 14 .child { 15 scroll-snap-align: start; 16 scroll-snap-stop: always; 17 width: 100%; 18 height: calc(100svh - 80px); 19 font-size: 30px; 20 } 21 .child:last-child { 22 background-image: linear-gradient(to right, black 1px, transparent 1px), 23 linear-gradient(to bottom, black 1px, transparent 1px); 24 background-size: 64px 64px; 25 height: 200%; 26 } 27 </style> 28 <div id="scroller"> 29 <div class="child">1</div> 30 <div class="child">2</div> 31 </div> 32 <script> 33 promise_test(async () => { 34 assert_equals(scroller.scrollTop, 0); 35 36 const scrollendPromise = new Promise(resolve => { 37 scroller.addEventListener("scrollend", resolve); 38 }); 39 40 const expectedPosition = 41 scroller.children[0].getBoundingClientRect().height + 100; 42 // Try to scroll downward, it will snap to a position inside 43 // the second child. 44 scroller.scrollTo(0, expectedPosition); 45 await scrollendPromise; 46 47 assert_equals(scroller.scrollTop, expectedPosition, 48 "The scroll position is the expected one"); 49 50 // Change the second child width, it will re-evaluate the snap position. 51 scroller.querySelector(":last-child").style.width = "99%"; 52 53 // Give a chance to scroll if it happens. 54 await new Promise(resolve => { 55 requestAnimationFrame(() => requestAnimationFrame(resolve)); 56 }); 57 58 assert_equals(scroller.scrollTop, expectedPosition, 59 "Should stay at the last snap point"); 60 }, "Keep the same snap position on overflowing-snap-area when re-snapping"); 61 </script>