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<!DOCTYPE html>
<meta name="viewport" content="width=device-width,initial-scale=1">
<link rel="help" href="https://drafts.csswg.org/css-scroll-snap/#re-snap" />
<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1978946">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
#scroller {
overflow-y: auto;
scroll-snap-type: y mandatory;
width: 100vw;
height: calc(100svh - 80px);
}
.child {
scroll-snap-align: start;
scroll-snap-stop: always;
width: 100%;
height: calc(100svh - 80px);
font-size: 30px;
}
.child:last-child {
background-image: linear-gradient(to right, black 1px, transparent 1px),
linear-gradient(to bottom, black 1px, transparent 1px);
background-size: 64px 64px;
height: 200%;
}
</style>
<div id="scroller">
<div class="child">1</div>
<div class="child">2</div>
</div>
<script>
promise_test(async () => {
assert_equals(scroller.scrollTop, 0);
const scrollendPromise = new Promise(resolve => {
scroller.addEventListener("scrollend", resolve);
});
const expectedPosition =
scroller.children[0].getBoundingClientRect().height + 100;
// Try to scroll downward, it will snap to a position inside
// the second child.
scroller.scrollTo(0, expectedPosition);
await scrollendPromise;
assert_equals(scroller.scrollTop, expectedPosition,
"The scroll position is the expected one");
// Change the second child width, it will re-evaluate the snap position.
scroller.querySelector(":last-child").style.width = "99%";
// Give a chance to scroll if it happens.
await new Promise(resolve => {
requestAnimationFrame(() => requestAnimationFrame(resolve));
});
assert_equals(scroller.scrollTop, expectedPosition,
"Should stay at the last snap point");
}, "Keep the same snap position on overflowing-snap-area when re-snapping");
</script>
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