JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://benpickles.github.com/onScreen/jquery.onscreen.js"></script>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
<div class="elem">CONTENT</div>
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<div class="elem">CONTENT</div>

CSS

.elem {
    padding: 1em;
    font-family: Helvetica;
    font-size: 18px;
    background: black;
    color: white;
    width: 100%;
}
.elem.last {
    background: red;
    color: white;
}

JavaScript

$(document).ready(function() {
    $(window).scroll(function() {

        $('.elem').removeClass("temp last")
        $('.elem').filter(":onScreen").addClass("temp")

        $(".temp").eq(-1).addClass("last")

    });
});