JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
    <li data-cat="one">test
    <li data-cat="one">test
    <li data-cat="two">test
    <li data-cat="three">test
    <li data-cat="three">test
    <li data-cat="three">test
</ul>

CSS

.active {
    color: red;
}

JavaScript

var list = $( '[data-cat]' ).get();
listSorted = jQuery.unique( list );
$( listSorted ).addClass('active');