JSFiddle - React, Tailwind, and code Playground

HTML

<span class="a"></span><span class="a"></span>
<span class="b"></span>
<span class="a"></span><span class="c"></span>
<span class="c"></span>

<div id="c"></div>
<tr id="Ok"></tr>

JavaScript

$.each(['a', 'b', 'c', 'xyz'], function(idx, cls) {
    $('#output').append('<p>'+cls+': '+$('.' + cls).length+'</p>');
});