JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<html>
<head></head>
<body>
<div id="" class="readmore-box">123</div>
<div id="" class="readmore-box">456</div>
<div id="" class="readmore-box">789</div>
</body>
</html>

JavaScript

$(function(){
	$('div.readmore-box').attr("id", "newId");
});