<!DOCTYPE html>
<html>
<head>
    <script>
        function processMessage(event)
        {
            fetch(event.data, { mode: "no-cors" }).then(() => {
                parent.postMessage("ok", "*");
            }, () => {
                parent.postMessage("ko", "*");
            });
        }
        window.addEventListener("message", processMessage, false);
    </script>
</head>
<body>
    <h3>The iframe making a same origin fetch call.</h3>
</body>
</html>
