JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
     <li id="slide-a" class="slide-li active-slide"><a href="#" >A</a></li>
     <li id="slide-b" class="slide-li"><a href="#" >B</a></li>
     <li id="slide-c" class="slide-li"><a href="#" >C</a></li                        
  </ul>

JavaScript

var active = $(".active-slide").attr("id");
console.log(active);