gymrooster_php/templates/dashboard.html.php

<?php require __DIR__ . '/../php/dashboard.php' ?>

<header>
  <h1>Gymrooster</h1>
  <h3>Welkom <?=$docent['naam']?></h3>
  <h3><?=date("D d M Y", strtotime($date))?></h3>
  <a href="/dashboard?date=<?=date("Y-m-d", strtotime("-1 day", strtotime($date)))?>">&lt;&nbsp;Dag eerder</a>
  <a href="/dashboard?date=<?=date("Y-m-d", strtotime("+1 day", strtotime($date)))?>">Dag later&nbsp;&gt;</a>
</header>

<form id="submitForm" action="update?date=<?=$date?>&docent=<?=$docent['id']?>" method="post">
  <textarea name="opmerking" placeholder="Opmerkingen"><?=$rooster['opmerking']?></textarea><br>
  <select name="locatie">
  <?php if ($rooster['locatie'] === "1"): ?>
    <option value="1">Binnen</option>
    <option value="2">Buiten</option>
  <?php else: ?>
    <option value="2">Buiten</option>
    <option value="1">Binnen</option>
  <?php endif; ?>
  </select>
  <button type="submit">Opslaan</button>
</form>

<script>
  document.getElementById('submitForm').addEventListener('submit', function(e) {
    document.querySelectorAll('#submitForm button')[0].innerHTML = "✓ Opgeslagen";
  });
</script>