使用jquery.rules时表单验证不起作用

<script src="https://cdn.jsdelivr.net/npm/jquery@3.6.0/dist/jquery.min.js"></script>
<script src="https://cdn.jsdelivr.net/jquery.validation/1.16.0/jquery.validate.min.js"></script>

<input type="text" name="username" required>

$("form").validate({
  rules: {
    username: "required"
  },
  messages: {
    username: "请输入用户名"
  }
});

<form id="myForm">
  <input type="text" name="username" required>
  <button type="submit">提交</button>
</form>

$("#myForm").validate({
  rules: {
    username: "required"
  },
  messages: {
    username: "请输入用户名"
  }
});

$("#myForm").validate({
  rules: {
    username: "required"
  },
  messages: {
    username: "请输入用户名"
  },
  submitHandler: function(form) {
    // 表单验证通过后的处理逻辑
    form.submit();
  }
});