third_party/web_platform_tests/intersection-observer/inline-client-rect.html

<!DOCTYPE html>
<meta name="viewport" content="width=device-width,initial-scale=1">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="./resources/intersection-observer-test-utils.js"></script>

<style>
pre, #log {
  position: absolute;
  top: 120px;
  left: 0;
}
#scroller {
  width: 250px;
  overflow: auto;
}
#overflow {
  width: 1000px;
}
.content {
  width: 100px;
  height: 20px;
  padding: 40px 0;
  text-align: center;
  background-color: grey;
  display: inline-block;
}
</style>

<div id="scroller">
  <div id="overflow">
    <span><div class="content">1</div></span>
    <span><div class="content">2</div></span>
    <span><div class="content">3</div></span>
    <span id="target"><div class="content">4</div></span>
    <span><div class="content">5</div></span>
  </div>
</div>

<script>
var vw = document.documentElement.clientWidth;
var vh = document.documentElement.clientHeight;

var entries = [];
var scroller, target, spaceWidth, targetOffsetLeft, targetOffsetTop;

runTestCycle(function() {
  scroller = document.getElementById("scroller");
  assert_true(!!scroller, "scroller exists");
  target = document.getElementById("target");
  assert_true(!!target, "target exists");
  var observer = new IntersectionObserver(function(changes) {
    entries = entries.concat(changes)
  });
  observer.observe(target);
  entries = entries.concat(observer.takeRecords());
  assert_equals(entries.length, 0, "No initial notifications.");
  runTestCycle(step0, "First rAF");
}, "Inline target");

function step0() {
  // Measure space width between two adjacent inlines.
  let nextEl = target.nextElementSibling;
  spaceWidth = nextEl.offsetLeft - target.offsetLeft - target.offsetWidth;
  // 8px body margin + 3 preceding siblings @ (100px width + spaceWidth) each
  targetOffsetLeft = 8 + 300 + (spaceWidth * 3);
  // 8px body margin + 40px top padding
  targetOffsetTop = 48;
  let left = targetOffsetLeft;
  let right = left + 100;
  let top = targetOffsetTop;
  let bottom = top + target.offsetHeight;

  scroller.scrollLeft = 90;
  runTestCycle(step1, "scroller.scrollLeft = 90");

  checkLastEntry(entries, 0, [left, right, top, bottom,
                              0, 0, 0, 0, 0, vw, 0, vh, false]);
}

function step1() {
  // -90px for scroll offset
  let left = targetOffsetLeft - 90;
  let right = left + 100;
  let top = targetOffsetTop;
  let bottom = top + target.offsetHeight;
  // 8px body margin + 250px client width of scroller
  let scrollerRight = 258;
  checkLastEntry(entries, 1, [left, right, top, bottom,
                              left, scrollerRight, top, bottom,
                              0, vw, 0, vh, true]);
}
</script>