formの中にscript

  <div class='inline'>
    <label class='ng emailSelf'>
      <input type='text' name='emailSelf' id='emailSelf'
        placeholder='メールアドレス' value='<?= $_POST["emailSelf"] ?>'>
      <?= $errors['emailSelf'] ?>
    </label>
    @
    <label class='ng emailAt'>
      <select>
        <option><?= join('</option><option>', $mailAts) ?></option>
      </select>
      <input type='text' name='emailAt' id='emailAt' style=''
        placeholder='メールドメイン' value='<?= $_POST["emailAt"] ?>'>
      <?= $errors['emailAt'] ?>
    </label>
  </div>
<script style='display: none;'>
$(function(){
    var email = $('div.inline label.emailAt');
    $('select', email).change(function(){
        $('input', email).val($(this).val());
    });
});
</script>