JSFiddle - React, Tailwind, and code Playground

HTML

<iframe id="iframe"></iframe>
<script>
    document.getElementById("iframe").contentWindow.document.write( "<html><head></head><body><div>The div</div></body></html>" );
</script>

JavaScript

var iframe = document.getElementById('iframe');
var doc = iframe.contentDocument || iframe.contentWindow.document;

var div = doc.getElementsByTagName('div')[0];

console.log('Did we find the iframe? ' + ($(div).closest('iframe').length > 0));