如何使用jQuery验证器添加错误消息

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

$(document).ready(function() {
  $("#myForm").validate({
    errorPlacement: function(error, element) {
      error.appendTo(element.parent());
    },
    errorElement: "span"
  });
});

label.error {
  color: red;
  font-size: 12px;
}

<form id="myForm">
  <input type="text" name="username" required>
  <span class="error-container"></span>
  <input type="email" name="email" email>
  <span class="error-container"></span>
  <button type="submit">提交</button>
</form>

$(document).ready(function() {
  $("#myForm").validate({
    errorPlacement: function(error, element) {
      error.appendTo(element.siblings(".error-container"));
    },
    errorElement: "span",
    messages: {
      username: {
        required: "请输入用户名"
      },
      email: {
        email: "请输入有效的邮箱地址"
      }
    }
  });
});