JSFiddle - React, Tailwind, and code Playground

HTML

<iframe id="one"></iframe>
<iframe id="two"></iframe>

CSS

body, html {
    height: 5000%;
}
iframe {
    position: relative;
    top: 150px;
}

JavaScript

function run() {
    var div = document.createElement('div'),
        scrollY = 'no';
    div.id = 'scrollY';
    document.body.appendChild(div);
    document.getElementById("scrollY").innerHTML = scrollY;
    window.parent.addEventListener('scroll', function() {
        scrollY = window.parent.pageYOffset;
        document.getElementById("scrollY").innerHTML = scrollY;
    });
}

frames[0].window.eval('(' + run.toString() + '())');
frames[1].window.eval('(' + run.toString() + '())');