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snap-area-capturing-remove-scroll-container.html
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<!DOCTYPE html>
<title>
When an element no longer captures snap positions (e.g., no longer
scrollable), then its currently captured snap areas must be reassigned.
</title>
<link rel="help" href="https://drafts.csswg.org/css-scroll-snap/#captures-snap-positions"/>
<meta name="viewport" content="user-scalable=no">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
div {
position: absolute;
margin: 0px;
}
html {
scroll-snap-type: y mandatory;
}
body {
margin: 0px;
}
#middle-scroller {
top: 100px;
height: 500px;
width: 500px;
overflow: scroll;
background-color: rgb(12, 61, 2);
scroll-snap-type: none;
}
#inner-scroller {
top: 200px;
height: 400px;
width: 400px;
overflow: scroll;
background-color: rgb(65, 139, 50);
scroll-snap-type: y mandatory;
}
.space {
width: 2000px;
height: 2000px;
}
#inner-snap-area {
top: 300px;
width: 200px;
height: 200px;
background-color: blue;
scroll-snap-align: start;
}
#document-snap-area {
top: 500px;
width: 200px;
height: 200px;
background-color: lightblue;
scroll-snap-align: start;
}
</style>
<div class="space"></div>
<div id="middle-scroller">
<div class="space"></div>
<div id="inner-scroller">
<div class="space"></div>
<div id="inner-snap-area"></div>
</div>
</div>
</div>
<div id="document-snap-area"></div>
<script>
// This tests that making a snap container no longer scrollable will reassign
// its snap areas to the next scrollable ancestor, per spec [1].
// [1] https://drafts.csswg.org/css-scroll-snap/#captures-snap-positions
test(() => {
const inner_scroller = document.getElementById("inner-scroller");
const middle_scroller = document.getElementById("middle-scroller");
const document_scroller = document.scrollingElement;
// Inner scroller should snap to its captured area.
// Middle scroller doesn't snap.
// Document scroller should snap to its only captured area.
inner_scroller.scrollBy(0,10);
middle_scroller.scrollBy(0, 10);
// Scroll to (0,600), where we would expect the inner snap area to be relative
// to the document scroller.
document_scroller.scrollTo(0, 600);
assert_equals(inner_scroller.scrollTop, 300);
assert_equals(middle_scroller.scrollTop, 10);
assert_equals(document_scroller.scrollTop, 500);
// Inner scroller is no longer a scroll container.
inner_scroller.style.setProperty("overflow", "visible");
assert_equals(inner_scroller.scrollTop, 0);
assert_equals(middle_scroller.scrollTop, 10);
assert_equals(document_scroller.scrollTop, 500);
// The new snap container is the middle scroller, which has snap-type 'none'.
// Per spec, the scroll container should capture snap positions even if it has
// snap-type 'none'.
// The middle scroller should not snap.
// The document scroller should still only snap to its captured snap area.
document_scroller.scrollBy(0, 100);
middle_scroller.scrollBy(0, 10);
assert_equals(inner_scroller.scrollTop, 0);
assert_equals(middle_scroller.scrollTop, 20);
assert_equals(document_scroller.scrollTop, 500);
// The scroll container should now be at the document level.
middle_scroller.style.setProperty("overflow", "visible");
document_scroller.scrollBy(0, -10);
assert_equals(inner_scroller.scrollTop, 0);
assert_equals(middle_scroller.scrollTop, 0);
// Check that the existing snap area did not get removed when reassigning
// the inner snap area.
assert_equals(document_scroller.scrollTop, 500);
// Check that the inner snap area got reassigned to the document.
document_scroller.scrollBy(0, 150);
assert_equals(document_scroller.scrollTop, 600);
}, 'Making a snap container not scrollable should promote the next scrollable\
ancestor to become a snap container.');
</script>