JSFiddle - React, Tailwind, and code Playground

HTML

<button>show height</button>
<div>Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et ea rebum. Stet clita kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet. Lorem ipsum dolor sit amet, consetetur </div>

JavaScript

$("div").css("display",'none');

$("div").data("finalHeight",$("div").css("height"));
$("div").slideDown(5000);

$("button").click(function() {
    var finalHeight = $("div").data("finalHeight");
    var str = 'height of the element will be ' + finalHeight;
    str += ' when the animation is complete';
    alert(str);
});