JSFiddle - React, Tailwind, and code Playground

HTML

<select id="month" name="month">
<option value="Jan">Jan</option>
<option value="Feb">Feb</option>
<option value="Mar">Mar</option>
<option value="Apr">Apr</option>
<option value="May">May</option>
<option value="Jun">Jun</option>
<option value="Jul">Jul</option>
<option value="Aug">Aug</option>
<option value="Sep">Sep</option>
<option value="Oct">Oct</option>
<option value="Nov">Nov</option>
<option value="Dec">Dec</option>
</select>

JavaScript

var monthSelect = document.getElementById("month");

monthSelect.onchange = function(){
  var thisValue = this.value;
  alert(thisValue);
};