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Test Info:
- This WPT test may be referenced by the following Test IDs:
- /css/css-anchor-position/anchor-scroll-013.html - WPT Dashboard Interop Dashboard
<!DOCTYPE html>
<meta charset="utf-8">
<title>Test that changing the default anchor updates the scroll container's scrollHeight</title>
<link rel="author" title="Ting-Yu Lin" href="mailto:tlin@mozilla.com">
<meta name="assert" content="The remembered scroll offset belongs to the default anchor it was captured for, so after the default anchor changes, the scroll container's scrollHeight should reflect the positioned element's new position.">
<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-a {
anchor-name: --a;
height: 20px;
background: orange;
}
#anchor-b {
anchor-name: --b;
width: 50px;
height: 20px;
background: purple;
}
#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-a"></div>
<div style="height: 300px"></div>
</div>
<div id="anchor-b"></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 anchorB = document.getElementById("anchor-b");
const positioned = document.getElementById("positioned");
// Scroll before the first frame, so the remembered scroll offset of --a is
// non-zero.
scroller2.scrollTop = 50;
await waitForAtLeastOneFrame();
// Switch the default anchor to one outside scroller2.
positioned.style.positionAnchor = "--b";
await waitForAtLeastOneFrame();
assert_equals(positioned.getBoundingClientRect().top,
anchorB.getBoundingClientRect().bottom,
"#positioned should be anchored to --b");
const scrollHeightAfterSwitch = scroller1.scrollHeight;
// Starting to generate boxes again is an anchor recalculation point.
positioned.style.display = "none";
await waitForAtLeastOneFrame();
positioned.style.display = "";
await waitForAtLeastOneFrame();
assert_equals(scrollHeightAfterSwitch, scroller1.scrollHeight,
"scroller1.scrollHeight after changing the default anchor should match the one after an anchor recalculation point");
}, "Changing the default anchor updates the scroller's scrollHeight");
</script>