JSFiddle - React, Tailwind, and code Playground

HTML

<ul id="names">
   <li id="aa" class="selected">aa</li>
   <li id="bb" class="selected">bb</li>
   <li id="cc">cc</li>
   <li id="dd">dd</li>
</ul>

JavaScript

var selectedID = $('#names li.selected').map(function(){
  return this.id;
}).get();
alert(selectedID);