JSFiddle - React, Tailwind, and code Playground

HTML

<div id="element1">element1</div>
<br>
<div id="element2">element1</div>

CSS

.red{
  background: red;
}

#element1, #element2{
  height: 100px;
  width: 200px;
  outline: 1px solid #ccc;
}

JavaScript

var element1 = $('#element1');
var element2 = $('#element2');

$(document).ready(function(){

//this below does not work
	element2.addClass("red");
  
//this below works
  element1.addClass("red");
});