JSFiddle - React, Tailwind, and code Playground

HTML

<div id="demo">...</div>

CSS

#demo {
  max-height: 0;
  overflow:hidden;
  transition: 2s max-height; background:red;
}

#demo.expand {
  max-height: 1000px;
}

JavaScript

$('#demo').on("transitionend", function(e) { 
    console.log($('#demo').height());
}).addClass('expand');