JSFiddle - React, Tailwind, and code Playground

HTML

<div class=a>im a div</div>
<div class=a>im a div</div>
<div class=a>im a div</div>

JavaScript

a=document.getElementsByClassName("a");
console.log("before: "+a.length);
a[1].className="b";
console.log("after: "+a.length);