How do you handle async operations inside an exception filter in NestJS, for example logging to a database?

Q: How do you handle async operations inside an exception filter in NestJS, for example logging to a database?

@Catch() export class AsyncLoggingFilter implements ExceptionFilter { constructor(private readonly auditLogService: AuditLogService) {} catch(exception: unknown, host: ArgumentsHost): void { const ctx = host.switchToHttp(); const req = ctx.getRequest (); const res = ctx.getResponse (); const status = exception instanceof HttpException ? exception.getStatus() : 500; const message = exception instanceof HttpException ? exception.message : 'Internal server error'; // 1. Send response FIRST — do not await anything before this res.status(status).json({ statusCode: status, message }); // 2. Fire-and-forget async logging — does not block the response this.auditLogService .logError({ url: req.url, status, message, userId: (req as any).user?.id, }) .catch(logErr => console.error('Audit log write failed', logErr) ); } } NestJS does not await the return value of catch() — async operations after sending the response are fire-and-forget. Always call res.status().json() before any await — delaying it causes request timeouts. Add a .catch() on the async log call so a logging failure does not throw an unhandled rejection. For critical auditing that must not be lost, use a message queue (Redis, RabbitMQ) instead of a direct DB write. Never make the HTTP response wait for the audit log — they are independent concerns.

Difficulty: 6/10

Exception Filters, Async Operations, NestJS Logging

NestJS does not await the return value of catch(). Send the HTTP response first, then fire-and-forget the async operation with a .catch() fallback to handle logging failures. Never await an async call before res.status().json() — doing so delays the HTTP response and can cause timeouts.

Fire-and-forget async logging inside a filter

Async filter operation rules:

1
NestJS does not await the return value of catch() — async operations after sending the response are fire-and-forget.
2

How do you handle async operations inside an exception filter in NestJS, for example logging to a database?

Difficulty: 6/10

Exception Filters, Async Operations, NestJS Logging

NestJS does not await the return value of catch(). Send the HTTP response first, then fire-and-forget the async operation with a .catch() fallback to handle logging failures. Never await an async call before res.status().json() — doing so delays the HTTP response and can cause timeouts.

Fire-and-forget async logging inside a filter

Async filter operation rules:

1
NestJS does not await the return value of catch() — async operations after sending the response are fire-and-forget.
2

How do you handle async operations inside an exception filter in NestJS, for example logging to a database?

NestJS does not await the return value of catch(). Send the HTTP response first, then fire-and-forget the async operation with a .catch() fallback to handle logging failures. Never await an async call before res.status().json() — doing so delays the HTTP response and can cause timeouts.

How do you handle async operations inside an exception filter in NestJS, for example logging to a database?

NestJS does not await the return value of catch(). Send the HTTP response first, then fire-and-forget the async operation with a .catch() fallback to handle logging failures. Never await an async call before res.status().json() — doing so delays the HTTP response and can cause timeouts.

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