JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8/themes/dot-luv/jquery-ui.css">
<table class="stripeMe">
<tr><td>Test</td></tr>
<tr><td>Test</td></tr>
<tr><td>Test</td></tr>
<tr><td>Test</td></tr>
<tr><td>Test</td></tr>
<tr><td>Test</td></tr>
<tr><td>Test</td></tr>
<tr><td>Test</td></tr>
<tr><td>Test</td></tr>
<tr><td>Test</td></tr>
<tr><td>Test</td></tr>
<tr><td>Test</td></tr>
<tr><td>Test</td></tr>
</table>

CSS

.alt { background-color: red; }

JavaScript

$(".stripeMe tr:nth-child(4n)").add(".stripeMe tr:nth-child(4n-1)").addClass("alt");