JSFiddle - React, Tailwind, and code Playground

CSS

html, body{
    height:200%;
}

JavaScript

if(document.attachEvent){
    document.attachEvent('onscroll', scrollEvent); 
}else if(document.addEventListener){
    document.addEventListener('scroll', scrollEvent, false); 
}

function scrollEvent(e){
    var scroll = document.body.scrollTop;
    
    var text = null;
    if (scroll < 50) {
        text = document.createTextNode('A');
    } else {
        text = document.createTextNode('B');
    }
    document.body.appendChild(text);
}