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<html>
<body>
<style>
#target {
width: 100%;
height: 100%;
}
#reflow {
width: 100%;
height: 10px;
background-color: red;
}
</style>
<div id="target"></div>
<div id="reflow"></div>
<script>
function listener(e) {
parent.postMessage({ eventType: e.type, targetName: e.target.localName }, "*");
}
window.addEventListener("message", function(aEvent) {
if (aEvent.data === "reflow") {
let reflow = document.getElementById("reflow");
reflow.style.display = "none";
reflow.getBoundingClientRect();
reflow.style.display = "block";
reflow.getBoundingClientRect();
// Now wait a bit to see if there is any unexpected events fired.
requestAnimationFrame(
() => parent.postMessage({ eventType: "reflowed" }, "*")
);
}
});
let target = document.getElementById("target");
target.addEventListener("mouseenter", listener);
target.addEventListener("mouseleave", listener);
let root = document.documentElement;
root.addEventListener("mouseenter", listener);
root.addEventListener("mouseleave", listener);
</script>
</body>
</html>