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);
  }
})