JSFiddle - React, Tailwind, and code Playground

HTML

<select id="mymenu" size="1">  
<option value="volvo">Volvo</option>
  <option value="saab">Saab</option>
  <option value="mercedes">Mercedes</option>
  <option value="audi" onclick ="changeClass1();">Audi</option>
</select>
<div id="ab">

</div>

JavaScript

var selectmenu=document.getElementById("mymenu")
 selectmenu.onchange=function(){ //run some code when "onchange" event fires
  var chosenoption=this.options[this.selectedIndex] //this refers to "selectmenu"
  if (chosenoption.value!="nothing"){
     if(chosenoption.value == "audi")
     {
document.getElementById('ab').innerHTML= 'new contents';
     }
  }
 }