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<!DOCTYPE html>
<style>
body {
margin: 0;
padding: 0;
}
#target {
position: absolute;
height: 40px;
width: 40px;
background-color: green;
}
</style>
<div id="target"></div>
<script>
let options = {
rootMargin: '40px 0px 0px 0px',
threshold: [1]
}
let observer = new IntersectionObserver((observations) => {
const lastObservation = observations[observations.length - 1];
window.top.postMessage({
isIntersecting: lastObservation.isIntersecting
}, "*");
}, options);
observer.observe(document.getElementById("target"));
</script>