JSFiddle - React, Tailwind, and code Playground

HTML

<div></div>
<footer></footer>

CSS

div {
    height: 1000px;
}

footer {
    height: 300px;
    background: blue;
    width: 100%;
}

JavaScript

window.onscroll = function(ev) {
    if ($(window).scrollTop() >= $(document).height() - $(window).height() - $('footer').height()) {
        alert("you're at the top of the footer");
    }
};