JSFiddle - React, Tailwind, and code Playground

HTML

<div id='aa'>aaaaaaaaa</div>

JavaScript

function findElement(wdw, id)
{
    var el = wdw.document.getElementById(id);
    if(el) return el;
    for(var i=0; i<wdw.frames.length; i++)
    {
        var el = findElement(wdw.frames[i].window, id);
        if(el) return el;
    }
    
    return null;
}

alert(findElement(window, "aa"));