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<!DOCTYPE html>
<link rel="help" href="https://drafts.csswg.org/css-scroll-snap-1/#scroll-snap-type" />
<title>Page scroll snapping</title>
<meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1">
<meta name="flags" content="should">
<meta name="assert"
content="Test passes if page operation doesn't skip content">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/resources/testdriver.js"></script>
<script src="/resources/testdriver-vendor.js"></script>
<script src="/resources/testdriver-actions.js"></script>
<script src="/dom/events/scrolling/scroll_support.js"></script>
<script src="../support/common.js"></script>
<style>
html, body {
margin: 0;
}
.scroller {
height: 100vh;
overflow: auto;
position: relative;
scroll-snap-type: y mandatory;
counter-reset: --page;
}
.gap {
height: 100vh;
}
.page {
counter-increment: --page;
height: 90vh;
scroll-snap-align: center;
padding: 8px;
position: relative;
--page: counter(--page);
}
.short {
height: 25vh;
}
.page > div::before {
content: "Page " counter(--page);
font-size: 1.5em;
}
.page > div {
box-sizing: border-box;
border: 3px solid black;
border-radius: 5px;
overflow: clip; /* Make sure font size doesn't cause pages to be larger than expected. */
padding: 8px;
height: 100%;
}
</style>
<div class="scroller" tabindex="0">
<div class="page">
<div>
<p>This tests what happens when you perform a paging scroll (e.g. space bar or page down key) with mandatory scroll snap.</p>
<p>When snapped to this page, pressing page down should not skip page 2.</p>
</div>
</div>
<div class="short page">
<div>
<p>This page should not be skipped by paging scroll operations.</p>
</div>
</div>
<div class="page">
<div>
<p>We must stop at this page before going to page 4.</p>
</div>
</div>
<div class="short page">
<div>
<p>Pages 4, 5, and 6 should be a single snap stop on page 5.</p>
</div>
</div>
<div class="short page">
<div>
<p>
This should be the snapped page when paging.
The next page operation should jump to page 7.
</p>
</div>
</div>
<div class="short page">
<div></div>
</div>
<div class="page">
<div>
<p>
The next page is further than a page away,
but there are no closer snap points
so it should be scrolled to next.
</p>
</div>
</div>
<div class="gap"></div>
<div class="page">
<div>
<p>
The last page
</p>
</div>
</div>
</div>
<script>
const scroller = document.querySelector(".scroller");
scrollTop = () => scroller.scrollTop;
async function snapTo(page) {
if (page == 1 && scroller.scrollTop == 0)
return;
let scrollEndPromise = waitForScrollEndFallbackToDelayWithoutScrollEvent(scroller);
scroller.scrollTop = 0;
await scrollEndPromise;
if (page > 1) {
scrollEndPromise = waitForScrollEndFallbackToDelayWithoutScrollEvent(scroller);
scroller.querySelector(`.page[data-page="${page}"]`).scrollIntoView({block: "center"});
await scrollEndPromise;
}
}
scroller.querySelectorAll('.page').forEach((div, index) => {
div.setAttribute("data-page", index + 1);
});
function visiblePages() {
return Array.prototype.slice.apply(
scroller.querySelectorAll('.page')).filter(
div => div.offsetTop >= scroller.scrollTop &&
div.offsetTop + div.offsetHeight <= scroller.scrollTop + scroller.clientHeight).map(
div => parseInt(div.getAttribute("data-page")));
}
async function pageDown() {
const scrollEndPromise = waitForScrollEndFallbackToDelayWithoutScrollEvent(scroller);
await keyPress(scroller, "Space");
await scrollEndPromise;
}
promise_test(async t => {
await snapTo(1);
assert_array_equals(visiblePages(), [1]);
await pageDown();
assert_array_equals(visiblePages(), [2]);
}, `Doesn't skip past small snappable content`);
promise_test(async t => {
await snapTo(2);
assert_array_equals(visiblePages(), [2]);
await pageDown();
assert_array_equals(visiblePages(), [3]);
}, `Doesn't skip past large snappable content`);
promise_test(async t => {
await snapTo(3);
assert_array_equals(visiblePages(), [3]);
await pageDown();
assert_array_equals(visiblePages(), [4, 5, 6]);
}, `Scrolls multiple smaller items into view`);
promise_test(async t => {
await snapTo(5);
assert_array_equals(visiblePages(), [4, 5, 6]);
await pageDown();
assert_array_equals(visiblePages(), [7]);
}, `Scrolls past items currently in view`);
promise_test(async t => {
await snapTo(7);
assert_array_equals(visiblePages(), [7]);
await pageDown();
assert_array_equals(visiblePages(), [8]);
}, `Scrolls more than a page if necessary`);
</script>
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