JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
  <li> hi </li>
  <li> hoi </li>
  <li> privyet </li>
  <li class="selected"> bonjour </li>
  <li> hallo </li>
</ul>

JavaScript

var elem = $('ul li.selected');
var index = $("ul li").index(elem);

var index2 = $("ul li.selected").index("ul li");

var index3 = $("ul li.selected").index();

alert( index + " " + index2 + " " + index3 );