JSFiddle - React, Tailwind, and code Playground

HTML

<select id="mySelect">
  <option value="div1">div1</option>
  <option value="div2">div2</option>
</select>
<div id="div1" style="background:red;height:100px;width:100px;">
  <form></form>
</div>
<div id="div2" style="display:none;background:blue;height:100px;width:100px;">
  <form></form>
</div>

JavaScript

document.getElementById("mySelect").addEventListener("change", myFunction);
function myFunction() {
    var x = document.getElementById("mySelect").value;
    if(x=="div1"){
    	document.getElementById("div1").style.display="block"; 
      document.getElementById("div2").style.display="none"; 
    }else if(x=="div2"){
    	document.getElementById("div2").style.display="block"; 
      document.getElementById("div1").style.display="none"; 
    }
}