css/css-scroll-snap/nested-scrollIntoView-snaps.html

<!DOCTYPE html>
<link rel="help" href="https://drafts.csswg.org/css-scroll-snap-1/#scroll-snap-type" />
<meta name="viewport" content="user-scalable=no">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
div {
  position: absolute;
}
:root {
  overflow: scroll;
  scroll-snap-type: both mandatory;
}
.scroller {
  overflow: scroll;
  scroll-snap-type: both mandatory;
  padding: 0px;
}
#outer {
  left: 1000px;
  top: 1000px;
  width: 600px;
  height: 600px;
}
#out-snap-1 {
  scroll-snap-align: start;
  left: 1200px;
  top: 1200px;
  width: 10px;
  height: 10px;
}
#out-snap-2 {
  scroll-snap-align: start;
  left: 1100px;
  top: 1100px;
  width: 10px;
  height: 10px;
}
#inner {
  left: 1000px;
  top: 1000px;
  width: 400px;
  height: 400px;
}
.space {
  left: 0px;
  top: 0px;
  width: 3000px;
  height: 3000px;
}
#target {
  scroll-snap-align: end;
  left: 800px;
  top: 800px;
  width: 200px;
  height: 200px;
}
</style>

<div class="space"></div>
<div id="out-snap-1"></div>
<div id="out-snap-2"></div>
<div class="scroller" id="outer">
  <div class="space"></div>
  <div class="scroller" id="inner">
    <div class="space"></div>
    <div id="target"></div>
  </div>
</div>

<script>
var outer = document.getElementById("outer");
var inner = document.getElementById("inner");
var target = document.getElementById("target");

test(() => {
  // Initial layout triggers a scroll snap. Reset position before calling
  // scrollIntoView.
  window.scrollTo(0, 0);
  outer.scrollTo(0, 0);
  inner.scrollTo(0, 0);

  target.scrollIntoView({inline: "start", block: "start"});
  // Although the scrollIntoView specified "start" as the alignment, the target
  // has "end" as its snap-alignment. So the inner scroller finishes with "end"
  // alignment
  assert_equals(inner.scrollLeft, 1000 - inner.clientWidth, "ScrollIntoView lands on the target's snap position regardless of the specified alignment.");
  assert_equals(inner.scrollTop, 1000 - inner.clientHeight, "ScrollIntoView lands on the target's snap position regardless of the specified alignment.");

  // Since there is no snap points defined in the outer scroller, the outer
  // scroller finishes with "start" alignment, as specified in scrollIntoView.
  // Note that the "start" alignment aligns the target's top-left corner
  //(inner.left + inner.clientWidth - target.width, inner.top + inner.clientHeight - target.height)
  // with the outer scroller's top-left corner.
  assert_equals(outer.scrollLeft, 800 + inner.clientWidth, "ScrollIntoView ends with the specified alignment if no snap position is specified.");
  assert_equals(outer.scrollTop, 800 + inner.clientHeight, "ScrollIntoView ends with the specified alignment if no snap position is specified.");

  // Although the scrollIntoView specified "start" as the alignment, the window
  // has two other elements with snap points. So the window finishes with the
  // closest snap point.
  assert_equals(window.scrollX, 1100, "ScrollIntoView lands on the snap position closest to the specified alignment.");
  assert_equals(window.scrollY, 1100, "ScrollIntoView lands on the snap position closest to the specified alignment.");
}, "All the scrollers affected by scrollIntoView should land on a snap position if one exists. Otherwise, land according to the specified alignment");
</script>