JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
    <span data-foo="initial content">Blabla</span>    
</div>

JavaScript

console.log($("span").data("foo")); //initial content
console.log($("#container").html()); //<span data-foo="initial content">Blabla</span>   

$("span").data("foo", "new content");
               
console.log($("span").data("foo")); //new content
console.log($("#container").html()); //<span data-foo="initial content">Blabla</span>   <----- ?!?!?!?!