How to automatically fill-in textarea after you choose from cascading dropdown menu?

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Javascript

SQL

HTML

PHP

Ajax

Hi guys, I have a 2 level dropdown menu, and a textarea, which I would like to get populated as I choose from the dropdown menu. I managed the dropdown menu to word, but I cannot get the textarea to be populated. 2 dropdown and the textarea relate to the same data table.

The textarea has a CKEditor in it

The PHP/SQL code works. I have a trouble getting the result into the textarea.

<form>
  <div class="form-group">
    <select class="form-control" name="page" id="page" onchange="FetchArticle(this.value)" required>
      <option value="">Select page...</option>
      <?php foreach ($results as $rsp) { ?>
          <option value="<?php echo $rsp["id"]; ?>"><?php echo $rsp["page_name"]; ?></option>
      <?php } ;
          ?>
    </select>
  </div>
  <div class="form-group">
    <select class="form-control" name="article" id="article" onchange="FetchArticleBody(this.value)" required>
      <option value="">Select article...</option>
    </select>
  </div>
  <div class="form-group">
    <textarea name="article_body" id="article_body" value=""></textarea>
  </div>
</form>

<script type="text/javascript">
  function FetchArticle(id){
    $('#article').html('');
    $.ajax({
      type:'post',
      url: 'ajaxdata.php',
      data: { page_id : id},
      success : function(data){
        $('#article').html(data);
      }
    })
  }
  function FetchArticleBody(id){
    $('#article_body').html('');
    $.ajax({
      type:'post',
      url: 'ajaxdata.php',
      data: { article : id},
      success : function(data){
        $('#article_body').html(data);
      }
    })
  }
</script>

<?php
include_once 'config.php';

    if(isset($_POST['page_id'])){
      $page_id = $_POST['page_id'];
    $sql = "SELECT * FROM articles WHERE page_id=:page_id";
    $stmt = $pdo->prepare($sql);
    $stmt->bindParam(":page_id", $param_page_id, PDO::PARAM_INT);
    $param_page_id = $page_id;
    $stmt->execute();
    $results = $stmt->fetchAll();
    foreach ($results as $rsp) {
      echo '<option value='.$rsp['id'].'>'.$rsp['article_name'].'</option>';
    }
  }
  if(isset($_POST['article'])){
  $id = $_POST['article'];
  $sql = "SELECT article_body FROM articles WHERE id=:article";
  $stmt1 = $pdo->prepare($sql);
  $stmt1->bindParam(":article", $param_id, PDO::PARAM_INT);
  $param_id = $id;
  $stmt1->execute();
  $results = $stmt1->fetchColumn();
  echo $results;
  }
 ?>

Any and all help is greatly appreciated!

What I have tried:

I have tried to put php fetch codes in different files. I have tried to change the id of the div with the textarea to "article_body" and put textarea in php fetch code.