JSFiddle - React, Tailwind, and code Playground

HTML

<div id="scroller" style="height:100px; width: 100px; overflow: auto">
    <div style="height:1000px;">
        <p>text</p>
    </div>
</div>

JavaScript

var scroller = document.getElementById('scroller');
var delta = 5;
var lastSc;

    //console.log(scroller.scrollTop, scrollHeight);
setInterval(function(){
    var sc = scroller.scrollTop + delta;
    scroller.scrollTop = sc;
    if (scroller.scrollTop === lastSc){
        delta = delta*(-1);
    }
    lastSc = scroller.scrollTop;
    //console.log(sc, scroller.scrollHeight);
}, 10);