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<!DOCTYPE html>
<style>
html, body {
margin: 0;
}
#target {
width: 100px;
height: 100px;
}
</style>
<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>