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Test Info:

<!DOCTYPE html>
<meta name="viewport" content="user-scalable=no">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
div {
position: absolute;
}
:root {
overflow: scroll;
scroll-snap-type: both mandatory;
}
.scroller {
overflow: scroll;
scroll-snap-type: both mandatory;
padding: 0px;
}
#outer {
left: 1000px;
top: 1000px;
width: 600px;
height: 600px;
}
#out-snap-1 {
scroll-snap-align: start;
left: 1200px;
top: 1200px;
width: 10px;
height: 10px;
}
#out-snap-2 {
scroll-snap-align: start;
left: 1100px;
top: 1100px;
width: 10px;
height: 10px;
}
#inner {
left: 1000px;
top: 1000px;
width: 400px;
height: 400px;
}
.space {
left: 0px;
top: 0px;
width: 3000px;
height: 3000px;
}
#target {
scroll-snap-align: end;
left: 800px;
top: 800px;
width: 200px;
height: 200px;
}
</style>
<div class="space"></div>
<div id="out-snap-1"></div>
<div id="out-snap-2"></div>
<div class="scroller" id="outer">
<div class="space"></div>
<div class="scroller" id="inner">
<div class="space"></div>
<div id="target"></div>
</div>
</div>
<script>
var outer = document.getElementById("outer");
var inner = document.getElementById("inner");
var target = document.getElementById("target");
test(() => {
// Initial layout triggers a scroll snap. Reset position before calling
// scrollIntoView.
window.scrollTo(0, 0);
outer.scrollTo(0, 0);
inner.scrollTo(0, 0);
target.scrollIntoView({inline: "start", block: "start"});
// Although the scrollIntoView specified "start" as the alignment, the target
// has "end" as its snap-alignment. So the inner scroller finishes with "end"
// alignment
assert_equals(inner.scrollLeft, 1000 - inner.clientWidth, "ScrollIntoView lands on the target's snap position regardless of the specified alignment.");
assert_equals(inner.scrollTop, 1000 - inner.clientHeight, "ScrollIntoView lands on the target's snap position regardless of the specified alignment.");
// Since there is no snap points defined in the outer scroller, the outer
// scroller finishes with "start" alignment, as specified in scrollIntoView.
// Note that the "start" alignment aligns the target's top-left corner
//(inner.left + inner.clientWidth - target.width, inner.top + inner.clientHeight - target.height)
// with the outer scroller's top-left corner.
assert_equals(outer.scrollLeft, 800 + inner.clientWidth, "ScrollIntoView ends with the specified alignment if no snap position is specified.");
assert_equals(outer.scrollTop, 800 + inner.clientHeight, "ScrollIntoView ends with the specified alignment if no snap position is specified.");
// Although the scrollIntoView specified "start" as the alignment, the window
// has two other elements with snap points. So the window finishes with the
// closest snap point.
assert_equals(window.scrollX, 1100, "ScrollIntoView lands on the snap position closest to the specified alignment.");
assert_equals(window.scrollY, 1100, "ScrollIntoView lands on the snap position closest to the specified alignment.");
}, "All the scrollers affected by scrollIntoView should land on a snap position if one exists. Otherwise, land according to the specified alignment");
</script>