Why should I use a centralized error handler instead of handling errors in each route?

A centralized error handler ensures every error response has the same structure, prevents code duplication, guarantees that 5xx errors are always logged, and makes it impossible to accidentally return a raw stack trace. Without it, each developer invents their own error format, some routes return different JSON shapes for the same error type, and some errors are silently swallowed. The centralized handler acts as a single source of truth for how errors become HTTP responses.

How do I handle async errors in Express without try/catch in every route?

In Express 4, wrap route handlers with an asyncHandler function that catches rejected promises and calls next(err). In Express 5 and later, async errors are caught automatically. The wrapper pattern is: const asyncHandler = fn => (req, res, next) => Promise.resolve(fn(req, res, next)).catch(next). Apply it to every async route handler so thrown errors and rejected promises flow to the error middleware without explicit try/catch blocks.

What information should I log vs return in error responses?

Log everything the developer needs to debug: full stack trace, database queries, internal service names, user ID, request body, and headers (with sensitive values redacted). Return only what the client needs to handle the error: HTTP status code, error code, human-readable message for 4xx errors, request ID for support correlation, and field-level validation details. Never return stack traces, database details, or internal service names to clients as they expose implementation details and potential security vulnerabilities.

How does Spring Boot @ControllerAdvice compare to Express error middleware?

Both serve the same purpose: centralizing error handling across all routes. Spring @ControllerAdvice uses @ExceptionHandler methods that match exception types via Java type hierarchy. Express uses middleware functions with four parameters that handle all errors passed via next(err). The Spring approach is more type-safe with compile-time exception matching. The Express approach is more flexible with runtime instance checks. Both support ProblemDetail/RFC 7807 responses natively in recent versions.

How should I test error handling in my API?

Write explicit tests for every error type: 404 for missing resources, 422 for validation failures with field-level errors, 409 for conflicts, 401 and 403 for auth errors, and 500 for unhandled exceptions. For each test, verify the HTTP status code, the response body structure matches your error schema, specific fields like error_code and detail are present and correct, and that 500 errors do not expose stack traces. Mock service methods to throw errors and verify the error handler transforms them correctly.

Consistent Error Handling Patterns