JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8/themes/dot-luv/jquery-ui.css">
<select id="idname" name="namename">
  <option>Option1</option>
  <option>Option2</option>
  <option>Option3</option>
  <option>Option4</option>
</select>

JavaScript

document.getElementById("idname").onchange = function() {
    alert("Selected Index: " + this.selectedIndex);
};