<ul id="comments"></ul>
<input type="text" id="text">
<button type="button" id="send">Отправить</button>
<script>
  const list = document.getElementById('comments');
  document.getElementById('send').addEventListener('click', () => {
    const text = document.getElementById('text').value.trim();
    if (!text) return;
    const li = document.createElement('li');
    li.textContent = text; // НЕ innerHTML с сырым вводом
    list.append(li);
    document.getElementById('text').value = '';
  });
</script>