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Test Info:

<!DOCTYPE html>
<title>
Not re-snap once after a scroll operation has finished without snapping
because the scroll destination was outside of the snap proximity threshold.
</title>
<!-- This test assumes that all major browsers' default scroll-snap proximity
thresholds are greater than 200px. -->
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
div {
position: absolute;
margin: 0;
}
#scroller {
height: 600px;
width: 600px;
overflow: hidden;
scroll-snap-type: y proximity;
}
.snap {
width: 300px;
height: 300px;
background-color: green;
scroll-snap-align: start;
}
.area {
width: 2000px;
height: 2000px;
}
</style>
<div id="scroller">
<div class="area"></div>
<div class="snap" style="top: 0px;"></div>
<div class="snap" style="top: 500px;"></div>
</div>
<script>
test(() => {
// The initial snap position is at (0, 0).
assert_equals(scroller.scrollTop, 0);
assert_equals(scroller.scrollLeft, 0);
// Scroll to a position where it's outside of the scroll-snap proximity
// threshold, so that it won't trigger snapping.
scroller.scrollTo(0, 250);
assert_equals(scroller.scrollTop, 250);
assert_equals(scroller.scrollLeft, 0);
// Changing the initial snap target position, but still it's outside of the
// threshold.
document.querySelectorAll(".snap")[0].style.top = "10px";
// Not re-snap to the last snap point.
assert_equals(scroller.scrollTop, 250);
assert_equals(scroller.scrollLeft, 0);
}, "Not re-snap once after a scroll operation has finished without snapping " +
"because the scroll destination was outside of the snap proximity threshold.");
</script>