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<!DOCTYPE html>
<title>
Updating the snap alignment of a snap container's content should make the snap
container resnap accordingly.
</title>
<link rel="help" href="https://drafts.csswg.org/css-scroll-snap/#re-snap" />
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
div {
position: absolute;
margin: 0;
}
#scroller {
height: 200px;
width: 200px;
overflow: hidden;
scroll-snap-type: both mandatory;
}
#initial-target {
width: 300px;
height: 300px;
top: 100px;
left: 100px;
background-color: green;
scroll-snap-align: start;
}
#other-target {
width: 300px;
height: 300px;
top: 300px;
left: 300px;
background-color: red;
scroll-snap-align: start;
}
.area {
width: 2000px;
height: 2000px;
}
.snap-area {
scroll-snap-align: start !important;
}
</style>
<div id="scroller">
<div class="area"></div>
<div id="initial-target"></div>
<div id="other-target"></div>
</div>
<script>
const initial_target = document.getElementById("initial-target");
const other_target = document.getElementById("other-target");
const scroller = document.getElementById("scroller");
function cleanup() {
initial_target.style.setProperty("scroll-snap-align", "start");
other_target.style.setProperty("scroll-snap-align", "start");
initial_target.removeAttribute("class");
}
test(t => {
t.add_cleanup(cleanup);
scroller.scrollTo(0,0);
assert_equals(scroller.scrollTop, 100);
assert_equals(scroller.scrollLeft, 100);
initial_target.style.setProperty("scroll-snap-align", "end");
// target.top + target.height - scroller.height
assert_equals(scroller.scrollTop, 200);
assert_equals(scroller.scrollLeft, 200);
}, "Changing the current target's snap alignment should make the scroller"
+ " resnap to it even if another snap position is closer to the current offset");
test(t => {
t.add_cleanup(cleanup);
scroller.scrollTo(0,0);
assert_equals(scroller.scrollTop, 100);
assert_equals(scroller.scrollLeft, 100);
initial_target.style.setProperty("scroll-snap-align", "none");
assert_equals(scroller.scrollTop, 300);
assert_equals(scroller.scrollLeft, 300);
}, "Removing the current target's snap alignment should make the scroller"
+ " resnap to a new snap area.");
test(t => {
t.add_cleanup(cleanup);
initial_target.style.setProperty("scroll-snap-align", "none");
other_target.style.setProperty("scroll-snap-align", "none");
scroller.scrollTo(0,0);
assert_equals(scroller.scrollTop, 0);
assert_equals(scroller.scrollLeft, 0);
initial_target.style.setProperty("scroll-snap-align", "start");
assert_equals(scroller.scrollTop, 100);
assert_equals(scroller.scrollLeft, 100);
}, "Changing an element snap alignment from none to start should make the"
+ "scroller resnap.");
test(t => {
t.add_cleanup(cleanup);
initial_target.style.setProperty("scroll-snap-align", "none");
other_target.style.setProperty("scroll-snap-align", "none");
scroller.scrollTo(0,0);
assert_equals(scroller.scrollTop, 0);
assert_equals(scroller.scrollLeft, 0);
initial_target.classList.add("snap-area");
assert_equals(scroller.scrollTop, 100);
assert_equals(scroller.scrollLeft, 100);
}, "Changing an element snap alignment from none to start by adding a class"
+ " should make the scroller resnap.");
</script>
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