I am the iframe
<button id="test" title="testing">Click me</button>

<script>
const button = document.getElementById("test");
	button.addEventListener("click", function() {
	window.parent.postMessage(JSON.stringify("button clicked"));
});

window.addEventListener("message", function (event) {
	console.log("my event",event.data)
	window.parent.postMessage(JSON.stringify(event));
});
</script>