notifications-delivered-in-order.html

<!doctype HTML>
<script src="../resources/testharness.js"></script>
<script src="../resources/testharnessreport.js"></script>

<style>
  div {
    width: 100px;
    height: 100px;
  }
</style>
<div id="observeme"></div>

<script>
test(() => {
  let previousNum = 0;
  for (let i = 1; i < 50; ++i) {
    new ResizeObserver(function() {
      assert_equals(previousNum + 1, i);
      previousNum = i;
    }).observe(observeme);
  }
  observeme.style.height = "110px";
}, "ResizeObserver notifications are delivered in order.");
</script>

chromium/third_party/blink/web_tests/resize-observer/notifications-delivered-in-order.html