JSFiddle - React, Tailwind, and code Playground

HTML

<textarea  id="inpt" cols="30" rows="10"></textarea>
<div><input type="submit" value="append" id="btn" style="width:60px;height:20px;background:grey" onclick="injectJS();"></div><br>
<iframe id="fr" name="fr" style="width:300px;height:300px;"></iframe>

JavaScript

var _script = document.createElement('div');
//_script.type = 'text/javascript';
var iFrame =  document.getElementById('fr'),
iFrameBody,
t = document.getElementById("inpt"),
btn = document.getElementById('btn');

window.injectJS =function () {
    var content = _script;
var val = document.getElementById('inpt').value;
if ( iFrame.contentDocument ) 
{ 
iFrameBody =iFrame.contentDocument.getElementsByTagName('body')[0];
}
else if ( iFrame.contentWindow ) 
{ 
iFrameBody = iFrame.contentWindow.document.getElementsByTagName('body')[0];
}
 content.innerHTML = val; 
 iFrameBody.appendChild(content);
 console.log(iFrameBody);    
}