第 19 课：提交失败时标记输入错误

<form id="lessonForm" novalidate>
  <label for="minutes">练习分钟数</label>
  <input id="minutes" name="minutes" type="number" min="1" required aria-describedby="minutes-help">
  <p id="minutes-help">请输入至少 1 分钟。</p>
  <button type="submit">提交</button>
</form>
<script>
const form = document.querySelector('#lessonForm');
const input = document.querySelector('#minutes');
form.addEventListener('submit', event => {
  if (!form.reportValidity()) {
    input.setAttribute('aria-invalid', 'true');
    event.preventDefault();
  }
});
input.addEventListener('input', () => input.removeAttribute('aria-invalid'));
</script>