JSFiddle - React, Tailwind, and code Playground

HTML

<button onclick="removeClass()">remove class</button>
<button onclick="addEl()">add element</button>

<div id="playground"></div>

CSS

.foo { color: red; }

#playground {
    margin: 10px;
    padding: 10px;
    border: 1px dotted #ccc;
}

JavaScript

var items = document.getElementsByClassName('foo');

function addEl(){
    playground.innerHTML += '<div class="foo">'+(new Date)+'</div>';
}

function removeClass(){
    var i = items.length;
    while( i-- ){
        if( items[i].classList ){
           items[i].classList.remove('foo');
        } else {
           items[i].className = (' '+items[i].className+' ').replace(' foo ', '');
        }
    }
}

addEl();