src/third_party/web_platform_tests/intersection-observer/resources/v2-subframe.html - cobalt - Git at Google

 <!DOCTYPE html>
 <div id="target">target</div>
 <script>
 var delay = 100;
 var results = [];

 function waitForNotification(f) {
   setTimeout(() => {
     requestAnimationFrame(function () {
       requestAnimationFrame(function () {
         setTimeout(f)
       })
     })
   }, delay)
 }

 window.addEventListener("message", event => {
   waitForNotification(() => {
     window.parent.postMessage(results.map(e => e.isVisible), "*");
     results = [];
   });
 });

 onload = () => {
   var target = document.getElementById("target");
   var observer = new IntersectionObserver(entries => {
     results = entries;
   }, {trackVisibility: true, delay: delay});
   observer.observe(document.getElementById("target"));
   window.parent.postMessage("", "*");
 };
 </script>
	<!DOCTYPE html>
	<div id="target">target</div>
	<script>
	var delay = 100;
	var results = [];

	function waitForNotification(f) {
	setTimeout(() => {
	requestAnimationFrame(function () {
	requestAnimationFrame(function () {
	setTimeout(f)
	})
	})
	}, delay)
	}

	window.addEventListener("message", event => {
	waitForNotification(() => {
	window.parent.postMessage(results.map(e => e.isVisible), "*");
	results = [];
	});
	});

	onload = () => {
	var target = document.getElementById("target");
	var observer = new IntersectionObserver(entries => {
	results = entries;
	}, {trackVisibility: true, delay: delay});
	observer.observe(document.getElementById("target"));
	window.parent.postMessage("", "*");
	};
	</script>