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<meta charset="utf-8">
<meta name="viewport" content="width=device-width, minimum-scale=1.0">
<title>Tests scroll anchoring interaction with smooth visual scrolling.</title>
<script src="apz_test_utils.js"></script>
<script src="apz_test_native_event_utils.js"></script>
<script src="/tests/SimpleTest/paint_listener.js"></script>
body { margin: 0 }
#target > div {
height: 500px;
<div id="target"></div>
<div class="spacer" style="height: 200vh"></div>
const utils = SpecialPowers.DOMWindowUtils;
const targetElement = document.getElementById("target");
async function test() {
const destY = window.scrollMaxY;
ok(destY > 0, "Should have some scroll range");
// Scroll to the bottom of the page.
window.scrollTo(0, destY);
is(window.scrollY, window.scrollMaxY, "Should be at the bottom");
// Register a TransformEnd observer so we can tell when the smooth scroll
// animation stops.
let transformEndPromise = promiseTransformEnd();
// Trigger smooth scrolling, and quickly insert an element which takes
// space into the DOM.
// It is important that it actually takes space so as to trigger scroll
// anchoring.
targetElement.scrollIntoView({ behavior: "smooth" });
// Wait for the TransformEnd.
await transformEndPromise;
// Give scroll offsets a chance to sync.
await promiseApzFlushedRepaints();
// Check that the async smooth scroll finished.
is(window.scrollY, 0, "Should've completed the smooth scroll without getting interrupted by scroll anchoring");
.then(subtestDone, subtestFailed);