JSFiddle - React, Tailwind, and code Playground

HTML

<div id="div1" data-foo></div>
<div id="div2" data-foo="yep"></div>
<div id="div3"></div>

JavaScript

alert( document.getElementById('div1').dataset.foo );
alert( document.getElementById('div2').dataset.foo );
alert( document.getElementById('div3').dataset.foo );