JSFiddle - React, Tailwind, and code Playground

HTML

<p>Expect <span>"on dragstart fired"</span> to be green when the button is dragged.</p>
<button draggable="true">button</button>

JavaScript

var element = document.querySelector("button");
var span = document.querySelector("span");

element.addEventListener("dragstart", function(event) {
    span.style.color = "green";
}, false);