captureUnderscoreErrorException should return the event ID like captureException

[Asghar-Lyft]

Problem Statement

The captureUnderscoreErrorException function in @sentry/nextjs returns Promise<void>, but the underlying captureException it calls internally returns the event ID. This makes it impossible to display a "Reference ID" to users on custom error pages when using the recommended Next.js error handling pattern.

Use Case

In our Next.js _error.tsx page, we want to display a Sentry event ID to users so they can reference it when contacting support:

CustomError.getInitialProps = async (pageContext: NextPageContext) => {
    // This doesn't return the event ID 😞
    await Sentry.captureUnderscoreErrorException(pageContext);
    
    // Sentry.lastEventId() also doesn't work in SDK v10.37.0 but works on SDK v8.3.0
    const eventId = Sentry.lastEventId(); // Always undefined. WHY???
    
    return { statusCode, eventId };
};

Solution Brainstorm

We have to manually replicate what captureUnderscoreErrorException does internally:

const error = pageContext.err;
if (error) {
    // This returns the event ID ✅
    const eventId = Sentry.captureException(error, {
        mechanism: {
            type: 'instrument',
            handled: false,
            data: { function: '_error.getInitialProps' },
        },
    });
}

Additional Context

• Sentry.lastEventId() no longer works in newer SDK due to the new scope isolation model
• This worked in older SDK versions where lastEventId() was updated globally
• The same issue likely applies to other capture* wrapper functions that don't return the event ID

Proposed Solution

Update captureUnderscoreErrorException to return the event ID:

// Current
export async function captureUnderscoreErrorException(contextOrProps: unknown): Promise<void>

// Proposed
export async function captureUnderscoreErrorException(contextOrProps: unknown): Promise<string | undefined>

Priority

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[linear]

JS-1638

[Asghar-Lyft]

Also when I search id:EVENT_ID in Sentry dashboard in All Issues tab, it doesn't list the issue and

• For the id returned by captureException it shows Error lading chart data
• I copied captureUnderscoreErrorException to my repo and changed it to return event ID, in Sentry dashboard search leads to Error fetching releases error

[andreiborza]

Hi @Asghar-Lyft, thanks. I think that's reasonable. Will take a look.

[andreiborza]

Also when I search id:EVENT_ID in Sentry dashboard in All Issues tab, it doesn't list the issue and

• For the id returned by captureException it shows Error lading chart data
• I copied captureUnderscoreErrorException to my repo and changed it to return event ID, in Sentry dashboard search leads to Error fetching releases error

The event Id is generated on the client and might not actually be the one that ends up in Sentry unless you specifically pass it on in the event.

Regardless, it sounds strange that you don't find anything by the id. If you can link your sentry project I can also take a look there.

[Asghar-Lyft]

@andreiborza I have a few different projects and they use different version of Next.js and Sentry, I don't want to add many details here, the important part is that

1. on Next.js v14.2.29 and SDK v8.3.0everything works well
2. but on Next.js v15.4.5 and SDK v10.37.0 only client-side error capturing works and server-side doesn't work well and I cannot find the event-id of the server-side error

Sentry.lastEventId() also doesn't work in SDK v10.37.0 but works on SDK v8.3.0