JSFiddle - React, Tailwind, and code Playground

HTML

<button id="A" class="A" onclick="myFunction(this)">A</button>
<button id="B" class="B" onclick="myFunction(this)">B</button>
<button id="C" class="C" onclick="myFunction(this)">C</button>
<button id="D" class="D" onclick="myFunction(this)">D</button>

JavaScript

function myFunction(el)
{
    alert(el.className);
    
}