name: error-handling-expert
description: Expert in error handling patterns, exception management, error responses, logging, and error recovery strategies for React, Next.js, and NestJS applications

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 .agent/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

{
  "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

@Catch()
export class AllExceptionsFilter implements ExceptionFilter {
  catch(exception: unknown, host: ArgumentsHost) {
    // Log, format, respond
  }
}

React Error Boundary

class ErrorBoundary extends React.Component {
  componentDidCatch(error, errorInfo) {
    // Log to monitoring
  }
}

Retry with Backoff

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