error-handling-fundamentals

Error Handling Fundamentals Review

"Errors are not failures — they're information. Handle them like the valuable data they are."

When to Apply

Activate this skill when reviewing:

• try/catch blocks
• Promise chains (.then/.catch)
• API error responses
• Form validation
• Network request handling
• User-facing error messages

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Review Checklist

Error Catching

• No empty catches: Is every catch block doing something meaningful?
• Proper scope: Are errors caught at the right level?
• Context added: Do errors include helpful debugging info?
• Finally used: Are cleanup operations in finally blocks?

User Experience

• User-friendly messages: Will users understand the error?
• No technical details exposed: Are stack traces hidden from users?
• Actionable feedback: Does the error tell users what to do next?
• Graceful degradation: Does the app still work partially on error?

Logging & Debugging

• Errors logged: Are errors recorded for debugging?
• Context in logs: Do logs include request ID, user ID, etc.?
• Severity levels: Are critical errors distinguished from warnings?

Recovery

• Retry logic: Should this operation retry on failure?
• Fallback values: Is there a sensible default on error?
• Loading states: Is the user informed while retrying?

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Common Mistakes (Anti-Patterns)

1. The Empty Catch (The Silent Killer)

❌ try {
     await submitForm();
   } catch (error) {
     // TODO: handle later (never happens)
   }

✅ try {
     await submitForm();
   } catch (error) {
     console.error('Form submission failed:', error);
     setError('Could not submit. Please try again.');
   }

2. Catching Too Early

❌ function getUser(id) {
     try {
       return database.query(id);
     } catch {
       return null; // Caller has no idea it failed
     }
   }

✅ function getUser(id) {
     return database.query(id); // Let caller decide
   }

   // In UI layer
   try {
     const user = await getUser(id);
   } catch (error) {
     showToast('Could not load user');
   }