JSFiddle - React, Tailwind, and code Playground

HTML

<form name="Form1">


<input type="text" name="KeyName" value="" />
</form>

JavaScript

document.onkeyup = KeyCheck;       

function KeyCheck(e)
{

   var KeyID = (window.event) ? event.keyCode : e.keyCode;

   alert(KeyID );
   switch(KeyID)

   {

      case 18:

      document.Form1.KeyName.value = "Alt";
       
      break; 

      case 17:

      document.Form1.KeyName.value = "Ctrl";

      break;

     
   }

}