JSFiddle - React, Tailwind, and code Playground

HTML

<div class="content"></div>
<div class="bottom-position"></div>

CSS

body {
    margin: 0;
    font-family: sans-serif;
}
.content {
    height: 1000px;
    background: #000;
}
.bottom-position {
    position: fixed;
    bottom: 0;
    right: 0;
    color: #fff;
}

JavaScript

var win = $(window);
var info = $('.bottom-position');
function onScroll() {
	var viewportBottom = win.scrollTop() + win.innerHeight();
    info.html('Bottom viewport at: ' + viewportBottom + 'px from top.');
};
win.on('scroll resize', onScroll);
onScroll();