iframe.html

<!doctype html>

<html lang="en">

<head>
    <meta charset="utf-8">
    <title></title>

</head>

<body style="background-color: orangered;">
    
    <h2>Iframe</h2>

    <iframe src="https://github.kadasi.eu/index.html?v4" style="width:250px;height:350px;"></iframe> 

    <script>
        var msgListener = window.addEventListener
                ? "addEventListener"
                : "attachEvent";
        var msgResend = window[msgListener];
        var messageEvent = msgListener === "attachEvent"
            ? "onmessage"
            : "message";
        msgResend(messageEvent, function (e) {
            
            if (e.origin !== 'https://github.kadasi.eu') return;
            
            if (e.data){
                parent.postMessage(e.data, '*')
            }	
            
        });
    </script>
</body>

</html>