JSFiddle - React, Tailwind, and code Playground

HTML

<form>
  <select class="sel1" onchange="change();">
    <option>Test1</option>
    <option>Test2</option>
    <option>Test3</option>
  </select>
  
  <input type="text" onchange="change();" name="was_auch_immer" class="inp">
  
  <select class="sel2" onchange="change();">
    <option>Blabla</option>
    <option>awd</option>
    <option>awdawd</option>
  </select>
</form>

<br>
<textarea id="test"></textarea>

JavaScript

function change() {
  var sel1 = document.querySelector('.sel1').value;
  var inp = document.querySelector('.inp').value;
  var sel2 = document.querySelector('.sel2').value;
  
  document.getElementById("test").value = sel1 + " " + inp + " " + sel2;
}