JSFiddle - React, Tailwind, and code Playground

HTML

<div>Can't see me!</div>

CSS

div {
  color: black;
  display: none; /* Comment or remove to trigger event. */
  transition: color 1s;
}

.go {
  color: red;
}

JavaScript

function huzzah(e) {
  alert('Huzzah! We got an end event!\n\n' +
        'It was a[n] "' + e.type + '" event');
}

var div = document.querySelector('div');
div.addEventListener('transitionend', huzzah);

window.setTimeout(function() {
  div.classList.add('go');
});