JSFiddle - React, Tailwind, and code Playground

JavaScript

function createFrame(sig)
{
    var frame = document.createElement("iframe");
    document.body.appendChild(frame);
    frame.contentWindow.HTMLElement.prototype.signature = sig;
    return frame;
}

function createAndGetElementIn(frame)
{
    var doc = frame.contentDocument;
    doc.body.innerHTML = "<div id='target'>Hello</div>";
    return doc.getElementById('target');
}

var aframe = createFrame("a");
var aelem = createAndGetElementIn(aframe);
console.log("aelem in aframe:" + aelem.signature);

var bframe = createFrame("b");
var belem = createAndGetElementIn(bframe);
console.log("belem in bframe:" + belem.signature);

aframe.contentDocument.body.appendChild(belem);
console.log("belem in aframe:" + belem.signature);