JSFiddle - React, Tailwind, and code Playground
HTML
<select>
<option value="1">Value1</option>
<option value="2">Value2</option>
<option value="3">Value3</option>
</select>
JavaScript
var oldValue = null;
$('select').change(function(){
s = $(this);
val = s.val();
if (val != null) {
alert(val);
}
})