JSFiddle - React, Tailwind, and code Playground

HTML

<div id="box"></div>
<p>Hover over the red bar</p>

CSS

#box {
    height: 20px;
    background: red;
    opacity: .1;
    transition: all 2s;
}
#box:hover { opacity: 1 }

JavaScript

$(function(){
    $("#box").on("transitionend MSTransitionEnd", function(e){
        alert(e.type);
    });
});