<html>
<body>
<script>
window.addEventListener("load", e => {
    try {
        var x = '<html><body>Success! The navigation was blocked<script type="text/javascript"> window.top.location = "http://localhost:8000/security/resources/should-not-have-loaded.html";' + '</scr' + 'ipt></body></html>';
        var bs64 = btoa(x);
        document.write('<iframe sandbox="allow-top-navigation allow-scripts" src="data:text/html;base64,' + bs64 + '"></iframe>')
    } catch (e) {
        console.log(e);
    }
});
</script>
</body>
</html>
