error-handling-expert

# Error Handling Expert Skill Expert in error handling patterns, exception management, error responses, logging, and error recovery strategies for React, Next.js, and NestJS applications. ## When to Use - Implementing error handling - Creating exception filters - Designing error responses - Setting up error logging - Implementing error recovery - Handling async errors - Creating error boundaries - Implementing retry logic ## Project Context Discovery Before providing guidance: 1. Check `.agents/SYSTEM/ARCHITECTURE.md` for error patterns 2. Review existing exception filters 3. Check for error monitoring (Sentry, Rollbar) 4. Review logging libraries (Winston, Pino) ## Core Principles ### Error Types **Application Errors:** 400, 401, 403, 404, 409, 422 **System Errors:** 500, 502, 503, 504 ### Error Response Format ```typescript { "error": { "code": "VALIDATION_ERROR", "message": "Validation failed", "details": [...], "timestamp": "2025-01-01T00:00:00Z", "path": "/api/users", "requestId": "req-123456" } } ``` ## Quick Patterns ### NestJS Exception Filter ```typescript @Catch() export class AllExceptionsFilter implements ExceptionFilter { catch(exception: unknown, host: ArgumentsHost) { // Log, format, respond } } ``` ### React Error Boundary ```typescript class ErrorBoundary extends React.Component { componentDidCatch(error, errorInfo) { // Log to monitoring } } ``` ### Retry with Backoff ```typescript async function retryWithBackoff<T>(fn, maxRetries = 3): Promise<T> ``` ## Best Practices - User-friendly messages, no sensitive info - Log all errors with context - Integrate error monitoring (Sentry) - Implement retry logic and circuit breakers - Provide fallback values - Test error cases ## Recovery Strategies 1. **Retry Logic** - Exponential backoff 2. **Circuit Breaker** - Prevent cascade failures 3. **Fallback Values** - Graceful degradation --- **For complete exception filter implementations, custom exceptions, validation pipe setup, error boundaries, circuit breaker pattern, logging integration, and database/API error patterns, see:** `references/full-guide.md`