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<!DOCTYPE html>
<link rel="help" href="https://drafts.csswg.org/css-scroll-snap/#re-snap" />
<meta name="viewport" content="width=device-width,initial-scale=1">
<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1946375">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
#scroller {
display: flex;
overflow-x: hidden;
scroll-snap-align: start;
scroll-snap-type: x mandatory;
width: 500px;
height: 200px;
position: absolute;
}
.child {
display: flex;
flex: 0 0 500px;
scroll-snap-align: start;
width: 500px;
height: 100%;
align-items: center;
justify-content: center;
font-size: 30px;
}
</style>
<div id="scroller">
<div class="child" style="background-color: blue;">1</div>
<div class="child" style="background-color: green;">2</div>
<div class="child" style="background-color: yellow;">3</div>
</div>
<script>
promise_test(async () => {
assert_equals(scroller.scrollLeft, 0, "The initial scroll position");
const scrollPromise = new Promise(resolve => {
scroller.addEventListener("scroll", resolve);
});
// Do an async scroll operation to the second child.
scroller.scrollTo({ left: 500, behavior: "smooth" });
// Wait a scroll event.
await scrollPromise;
// Assuming that the current scroll position is not yet the scroll
// destination, i.e. during the async scroll is runnig try to do
// a new async scroll operation to the third child.
const scrollendPromise = new Promise(resolve => {
scroller.addEventListener("scrollend", resolve);
});
scroller.scrollTo({ left: 1000, behavior: "smooth" });
await scrollendPromise;
assert_equals(scroller.scrollLeft, 1000,
"Now the scroll position should be 1000px");
// Change a child element width so that re-snapping will happen.
document.querySelectorAll(".child")[0].style.width = "501px";
assert_equals(scroller.scrollLeft, 1000, "The scroll position should stay");
});
</script>
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