TypeError: Cannot read private member #headersList from an object whose class did not declare it

[kumargauravin]

Using App Router when using next/headers getting this on Node 20.16.0 Linux EC2 instance.

const headersList = headers();

this is what I am using in page.tsx

getting this on server. Server is expecting headers from SSO FR. Next 14.2.3 React 18.3.1

0|dashboar | TypeError: Cannot read private member #headersList from an object whose class did not declare it
0|dashboar | at [nodejs.util.inspect.custom] (node:internal/deps/undici/undici:8647:64)
0|dashboar | at formatValue (node:internal/util/inspect:806:19)
0|dashboar | at inspect (node:internal/util/inspect:365:10)
0|dashboar | at formatWithOptionsInternal (node:internal/util/inspect:2304:40)
0|dashboar | at formatWithOptions (node:internal/util/inspect:2166:10)
0|dashboar | at console.value (node:internal/console/constructor:349:14)
0|dashboar | at console.log (node:internal/console/constructor:386:61)
0|dashboar | at d (/apps/opt/data/sor-nbs-recon-dashboard-service-ui/dist/server/app/new-user/page.js:1:2693)
0|dashboar | at eh (/apps/opt/data/sor-nbs-recon-dashboard-service-ui/node_modules/next/dist/compiled/next-server/app-page.runtime.prod.js:12:134786)
0|dashboar | at e (/apps/opt/data/sor-nbs-recon-dashboard-service-ui/node_modules/next/dist/compiled/next-server/app-page.runtime.prod.js:12:137671) {
0|dashboar | digest: '463973562'
0|dashboar | }

[Juneezee]

Do you also get the error locally with next dev?

[StephenTangCook]

I started seeing this error today as well. @kumargauravin are you saying that console.log of the headers actually fixes the issue?? 😖

[kumargauravin]

No I said do not use the object directly use its functions to iterate error comes when for example you are trying to console.log(headersList) in this case

[kumargauravin]

If you use headersList.(iterative functions) provided by Headers it is all working good, something to do with how a static member of a class has to be exposed seems like more abstraction added.

[StephenTangCook]

Ah, I see! Thanks!

[mobeigi]

Ran into same issue, all I did was try to console.log() the headers in a server component.

As a workaround this works without throwing the exception:

const headerList = headers();
for (const [key, value] of headerList.entries()) {
  console.log(`${key}: ${value}`);
}

[ARiyou2000]

I still have the problem even after doing all that. What is the actual fix?

[kumargauravin]

Can you share your snippet! Whatever property you want to read from Headers do not use directly but using functions exposed by the instance.

[nyeoni]

I resolved the issue by removing console.log('[Page] headers', headers()). Thanks!

[kumargauravin]

Hi, Yes as headers have private members which were getting accessed. If you need you can iterate using functions provided than console will also work. Regards, Kumar

…

On Tue, Sep 24, 2024 at 12:00 PM Nayeon Kim (Jupi) ***@***.***> wrote: I resolved the issue by removing console.log('[Page] headers', headers()). Thanks! — Reply to this email directly, view it on GitHub <#68849 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ADK64R3Z76T44SSXIS2VRYDZYGEBVAVCNFSM6AAAAABMO3SKX6VHI2DSMVQWIX3LMV43URDJONRXK43TNFXW4Q3PNVWWK3TUHMYTANZUGEZDSNI> . You are receiving this because you were mentioned.Message ID: <vercel/next .***@***.***>

[rodrigopa]

Object.fromEntries(await headers());

[rodrigopsofto]

or
const headersList = new Headers(await headers());