css/css-scroll-snap/snap-inline-block.html

<!DOCTYPE html>
<link rel="help" href="https://drafts.csswg.org/css-scroll-snap-1/#scroll-snap-type" />
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
div {
  position: absolute;
  margin: 0px;
}
#scroller {
  width: 400px;
  height: 350px;
  overflow: scroll;
  scroll-snap-type: both mandatory;
}
#space {
  width: 1000px;
  height: 1000px;
}
#target {
  width: 200px;
  height: 200px;
  left: 300px;
  top: 300px;
}
</style>

<div id="scroller">
  <div id="space"></div>
  <div id="target"></div>
</div>

<script>
const scroller_width = scroller.clientWidth;
const scroller_height = scroller.clientHeight;
[
  ["horizontal-tb", 300,                  500 - scroller_height],
  ["vertical-lr",   500 - scroller_width, 300],
  ["vertical-rl",   scroller_width - 700, 300]
].forEach(([writing_mode, left, top]) => {
  test(() => {
    const target_left = getComputedStyle(target).left;
    scroller.style.writingMode = writing_mode;
    target.style.scrollSnapAlign = "end start";
    if (writing_mode == "vertical-rl") {
      target.style.left = (scroller_width - 700) + "px";
      scroller.scrollTo(-500, 0);
    } else {
      scroller.scrollTo(0, 0);
    }
    assert_equals(scroller.scrollLeft, left, "aligns correctly on x");
    assert_equals(scroller.scrollTop, top, "aligns correctly on y");
    target.style.left = target_left;
    scroller.style.writingMode = "";
  }, "Snaps correctly for " + writing_mode +
     " writing mode with 'scroll-snap-align: end start' alignment");
});

[
  ["horizontal-tb", 500 - scroller_width,     300],
  ["vertical-lr",   300,                      500 - scroller_height],
  ["vertical-rl",   target.clientWidth - 700, 500 - scroller_height]
].forEach(([writing_mode, left, top]) => {
  test(() => {
    const target_left = getComputedStyle(target).left;
    scroller.style.writingMode = writing_mode;
    target.style.scrollSnapAlign = "start end";
    if (writing_mode == "vertical-rl") {
      target.style.left = (scroller_width - 700) + "px";
      scroller.scrollTo(-500, 0);
    } else {
      scroller.scrollTo(0, 0);
    }
    assert_equals(scroller.scrollLeft, left, "aligns correctly on x");
    assert_equals(scroller.scrollTop, top, "aligns correctly on y");
    target.style.left = target_left;
    scroller.style.writingMode = "";
  }, "Snaps correctly for " + writing_mode +
     " writing mode with 'scroll-snap-align: start end' alignment");
});

test(() => {
  const target_left = getComputedStyle(target).left;
  scroller.style.direction = "rtl";
  target.style.scrollSnapAlign = "end start";
  target.style.left = (scroller_width - 700) + "px";

  scroller.scrollTo(-500, 0);
  assert_equals(scroller.scrollLeft, target.clientWidth - 700,
                "aligns correctly on x");
  assert_equals(scroller.scrollTop, 500 - scroller_height,
                "aligns correctly on y");

  target.style.left = target_left;
  scroller.style.direction = "";
}, "Snaps correctly for 'direction: rtl' with 'scroll-snap-align: end start' " +
   "alignment");

test(() => {
  const target_left = getComputedStyle(target).left;
  scroller.style.direction = "rtl";
  target.style.scrollSnapAlign = "start end";
  target.style.left = (scroller_width - 700) + "px";

  scroller.scrollTo(-500, 0);
  assert_equals(scroller.scrollLeft, scroller_width - 700,
                "aligns correctly on x");
  assert_equals(scroller.scrollTop, 300, "aligns correctly on y");

  target.style.left = target_left;
  scroller.style.direction = "";
}, "Snaps correctly for 'direction: rtl' with 'scroll-snap-align: start end' " +
   "alignment");

</script>