JSFiddle - React, Tailwind, and code Playground
HTML
<select class="wide" id="selectBox" name="option">
<optgroup label="Common">
<option value="one">One</option>
<option value="two">Two</option>
<option value="three">Three</option>
</optgroup>
<optgroup label="Less Common">
<option value="other">Other</option>
</optgroup>
</select>
JavaScript
$('selectBox').addEvent('change',function() {
alert(this.get("value"));
alert(this.getSelected().get("value"));
});