问题

我对TypeScript还很陌生，正在尝试使用`nextjs`和`rtk query`以及`antd`。但在尝试访问`useLoginMutation`中的`error`属性`error.data.message`时，它显示`error.data`的类型为`unknown`。

到目前为止，我尝试了使用类型守卫函数。

```typescript
import { FetchBaseQueryError } from "@reduxjs/toolkit/dist/query";

export default function isFetchBaseQueryError(
    error: unknown
): error is FetchBaseQueryError {
    return typeof error === "object" && error != null && "status" in error;
}

if (!isLoginLoading && error) {
    if (isFetchBaseQueryError(error)) {
        notification.error({
            message: "登录失败",
            description: error.data.message, // 这行代码导致错误
        });
    }
}

<details>
<summary>英文:</summary>

I am new to typescript and trying out `nextjs` and `rtk query` with `antd`.  By when trying to access `error` in `useLoginMutation` inside properties `error.data.message` , it shows `error.data` is type `unknown` .

What I have tried so far is I used a type guard function.

import { FetchBaseQueryError } from "@reduxjs/toolkit/dist/query";

export default function isFetchBaseQueryError(
error: unknown
): error is FetchBaseQueryError {
return typeof error === "object" && error != null && "status" in error;
}

if (!isLoginLoading && error) {
if (isFetchBaseQueryError(error)) {
notification.error({
message: "Login Failed",
description: error.data.message, // this line is causing error
});
}
}

</details>


# 答案1
**得分**: 2

```ts
import get from 'lodash/get'

function isFetchBaseQueryError(
  error: unknown
): error is FetchBaseQueryError & { data: { message: string } } {
  return (
    typeof error === "object" &&
    error != null &&
    "status" in error &&
    "data" in error &&
    !!get(error, "data.message") // 确保 data.message 存在
  );
}

const error = { data: { message: "message" }, status: "403" };
if (isFetchBaseQueryError(error)) {
  console.log(error.data.message);
}

const error1 = { status: "403" };
if (isFetchBaseQueryError(error1)) {
  console.log(error.data.message);
} else {
  console.log("data.message not defined");
}

import get from 'lodash/get'

function isFetchBaseQueryError(
  error: unknown
): error is FetchBaseQueryError & { data: { message: string } } {
  return (
    typeof error === "object" &&
    error != null &&
    "status" in error &&
    "data" in error &&
    !!get(error, "data.message") // make sure data.message exists
  );
}

const error = { data: { message: "message" }, status: "403" };
if (isFetchBaseQueryError(error)) {
  console.log(error.data.message);
}

const error1 = { status: "403" };
if (isFetchBaseQueryError(error1)) {
  console.log(error.data.message);
} else {
  console.log("data.message not defined");
}