third_party/web_platform_tests/intersection-observer/observer-without-js-reference.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>
/* Cobalt does not implement HTML5 spec for body margin. */
body {
  margin: 8px;
}
pre, #log {
  position: absolute;
  top: 0;
  left: 200px;
}
.spacer {
  /* Cobalt does not support calc */
  height: 100vh;
}
#target {
  width: 100px;
  height: 100px;
  background-color: green;
  /* Adjust for subtracted 100px in class=spacer */
  margin-top: 100px;
}
</style>
<div class="spacer"></div>
<div id="target"></div>
<div class="spacer"></div>

<script>
var entries = [];

runTestCycle(function() {
  var target = document.getElementById("target");
  assert_true(!!target, "Target exists");
  function createObserver() {
    new IntersectionObserver(function(changes) {
      entries = entries.concat(changes);
      window.testRunner.DoNonMeasuredLayout();
    }).observe(target);
  }
  createObserver();
  runTestCycle(step0, "First rAF");
}, "IntersectionObserver that is unreachable in js should still generate notifications.");
window.testRunner.DoNonMeasuredLayout();
window.testRunner.DoNonMeasuredLayout();

function step0() {
  document.getElementById("target").style.marginTop = "-200px";
  //document.scrollingElement.scrollTop = 300;
  runTestCycle(step1, "document.scrollingElement.scrollTop = 300");
  assert_equals(entries.length, 1, "One notification.");
}

function step1() {
  document.getElementById("target").style.marginTop = "100px";
  //document.scrollingElement.scrollTop = 0;
  assert_equals(entries.length, 2, "Two notifications.");
}
</script>