类型错误：无法获取 mern

如何解决类型错误：无法获取 mern

我正在学习“React、NodeJS、Express 和 MongoDB - MERN 全栈指南”部分“将 React.js 前端连接到后端”。任何人都可以指导我为什么会收到此错误？每当我更新或删除一个地方时，它都会显示错误：TypeError: Failed to fetch I can do about that?

const UserPlaces = () => {
const [loadedplaces,setLoadedplaces] = useState();
const { isLoading,error,sendRequest,clearError } = useHttpClient();

const userId = useParams().userId;

useEffect(() => {
    const fetchPlaces = async () => {
        try {
            const responseData = await sendRequest(
                `http://localhost:5000/api/places/user/${userId}`
            );
            setLoadedplaces(responseData.places);
        } catch (err) { }
    };
    fetchPlaces();

},[sendRequest,userId]);

const placeDeletedHandler = deletedplaceId => {
    setLoadedplaces(prevPlaces =>
        prevPlaces.filter(place => place.id !== deletedplaceId)
    );
};

return (
    <React.Fragment>
        <ErrorModal error={error} onClear={clearError} />
        {isLoading && (
            <div className="center">
                <LoadingSpinner />
            </div>
        )}
        {!isLoading && loadedplaces && <PlaceList items={loadedplaces} onDeletePlace={placeDeletedHandler} />}
    </React.Fragment>
);
};

export default UserPlaces;

前端：https://github.com/sharjeelyunus/peek-mern 后端：https://github.com/sharjeelyunus/peek-mern-api

解决方法

找到答案：那是内核错误。你只需要添加 cors。

var cors = require('cors');

app.use(cors(),(req,res,next) = {}