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Test Info:
- This WPT test may be referenced by the following Test IDs:
- /css/css-anchor-position/anchor-scroll-014.html - WPT Dashboard Interop Dashboard
<!DOCTYPE html>
<meta charset="utf-8">
<title>Test that reframing the default anchor keeps the remembered scroll offset</title>
<link rel="author" title="Ting-Yu Lin" href="mailto:tlin@mozilla.com">
<meta name="assert" content="Changing the default anchor's display type isn't an anchor recalculation point for the positioned element, so its remembered scroll offset is kept, and the scroll container's scrollHeight doesn't change.">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/common/rendering-utils.js"></script>
<style>
#scroller1 {
width: 200px;
height: 200px;
position: relative;
overflow: scroll;
}
#scroller2 {
width: 100px;
height: 100px;
overflow: scroll;
}
#anchor {
anchor-name: --a;
height: 20px;
background: orange;
}
#positioned {
position: absolute;
position-anchor: --a;
position-visibility: always;
left: 120px;
top: anchor(bottom);
width: 50px;
height: 20px;
background: lime;
}
#overflow {
/* Overflows #positioned, so it determines scroller1's scrollHeight. */
width: 10px;
height: 400px;
background: cyan;
}
</style>
<div id="scroller1">
<div style="height: 100px"></div>
<div id="scroller2">
<div style="height: 100px"></div>
<div id="anchor"></div>
<div style="height: 300px"></div>
</div>
<div style="height: 100px"></div>
<div id="positioned"><div id="overflow"></div></div>
</div>
<script>
promise_test(async () => {
const scroller1 = document.getElementById("scroller1");
const scroller2 = document.getElementById("scroller2");
const anchor = document.getElementById("anchor");
const positioned = document.getElementById("positioned");
await waitForAtLeastOneFrame();
// Scroll after the remembered scroll offset is captured, so #positioned has
// a default scroll shift.
scroller2.scrollTop = 50;
await waitForAtLeastOneFrame();
const scrollHeightBeforeReframe = scroller1.scrollHeight;
// Change the anchor's display type, and then reflow #positioned.
anchor.style.display = "flex";
await waitForAtLeastOneFrame();
positioned.style.minWidth = "1px";
await waitForAtLeastOneFrame();
assert_equals(positioned.getBoundingClientRect().top,
anchor.getBoundingClientRect().bottom,
"#positioned should still be anchored to #anchor");
assert_equals(scroller1.scrollHeight, scrollHeightBeforeReframe,
"scroller1.scrollHeight shouldn't change after changing the anchor's display type");
}, "Changing the default anchor's display type keeps the remembered scroll offset");
</script>