Node.js 如何在Expressjs中向用户显示此错误

如何访问名字、姓氏、电子邮件和密码。 示例：如何访问firstname是否存在并向用户显示错误，如firstname.msg

[{"firstname":{"value":"","msg":"Firstname is required","param":"firstname","location":"body"},"lastname":{"value":"","msg":"Lastname must not contain number or symbol","param":"lastname","location":"body"},"email":{"value":"","msg":"Email is required","param":"email","location":"body"},"password":{"value":"","msg":"Password is required","param":"password","location":"body"}}]

---

将数组保存到变量，例如

结果

。然后使用

.map（）；如果是，请将它们保存到新的
错误
数组中。如果未定义
msg
属性，则返回
undefined

然后，我们使用
.filter（）
立即删除
未定义的任何元素
，将
错误
数组仅保留与
结果
数组中的
msg
字段相等的字符串元素

最后，我们检查
errors
数组中是否有元素，如果有，则返回第一个元素（错误消息）；在express中，它将类似于：

if（errors.length>0）返回res.status（400.json）（errors[0]）

这将始终返回函数遇到的第一个错误

const results = [{"firstname":{"value":"","msg":"Firstname is required","param":"firstname","location":"body"},"lastname":{"value":"","msg":"Lastname must not contain number or symbol","param":"lastname","location":"body"},"email":{"value":"","msg":"Email is required","param":"email","location":"body"},"password":{"value":"","msg":"Password is required","param":"password","location":"body"}}]

const errors = results
    .map(({ firstname, lastname, email, password }) => {
        if(firstname.msg) return firstname.msg;
        else if (lastname.msg) return lastname.msg;
        else if (email.msg) return email.msg;
        else if (password.msg) return password.msg;
        else return;
    })
    .filter(error => error);

if(errors.length > 0) return errors[0];