JSFiddle - React, Tailwind, and code Playground

HTML

<div id="parent">
    <div id="box">box</div>
</div>

<div id="height">Before display</div>
<div id="height1">After display</div>

CSS

#box {
    box-sizing: border-box;
    height: 40px;
    border: 1px solid #000;
    padding: 10px;
    width: 100px;
}

#parent {
    display: none;
}

JavaScript

$(document).ready(function() {
    $('#height').text(parseInt($('#box').css('height')));
    
    setTimeout(function() {
        $('#parent').show();
    }, 500);
    
    setTimeout(function() {
        $('#height1').text(parseInt($('#box').css('height')));
    }, 1000);
});