JSFiddle - React, Tailwind, and code Playground

HTML

<form id="myform">
<table><tr>
<td valign=top>Nieuwsbrief:</td>
<td>
<select id="NieuwsbriefSelect" name="show">
    <option size =30 selected>Select</option>
    <option value="test">test</option>
    <option value="test2">test2</option>
    <option value="alles weer testen">alles weer testen</option>
    <option value="testje">testje</option>
    <option value="Statusupdate week 6">Statusupdate week 6</option>
</select>
    </td>
    </tr><tr><td>
    Bericht:</td><td align="left"><textarea name="content" cols="50" rows="15"></textarea></td></tr>
</table>
   

</form>

JavaScript

var request;
$(document).ready(function() {

 $('#NieuwsbriefSelect').change(function() {
      //send Ajax call to get new contents
      var selected_text = $(this).val();
      // setup some local variables
      var $form = $("#myform");
      // let's select and cache all the fields
      var $inputs = $form.find("input, select, button, textarea");
      // serialize the data in the form
      var serializedData = $form.serialize();
      alert(serializedData);
      // fire off the request to /get_my_contents.php
      var request = $.ajax({
        url: "/get_my_contents.php",
        type: "post",
        data: serializedData
       });


       // callback handler that will be called on success
       request.done(function (response, textStatus, jqXHR){
        //populate the TextArea
        $("textarea[name='content']").html(response);
       });


    });

});