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