output-error-try-catch

Fix Try-Catch Anti-Pattern

Overview

This skill helps diagnose and fix a common anti-pattern where step calls are wrapped in try-catch blocks. This prevents Output SDK's retry mechanism from working properly and can lead to confusing error behavior.

When to Use This Skill

You're seeing:

• Retries not working as expected
• Errors being swallowed silently
• Unexpected FatalError wrapping
• Step failures not triggering retry policies
• Errors being caught and re-thrown incorrectly

Root Cause

When you wrap step calls in try-catch blocks, you intercept errors before the Output SDK retry mechanism can handle them. This defeats the built-in retry logic and can cause:

1. Retries not happening: The error is caught, so the framework doesn't know to retry
2. Wrong error classification: Re-throwing as FatalError prevents retries entirely
3. Lost error context: Original error details may be lost in the catch block

Symptoms

Pattern 1: Errors Swallowed

// WRONG: Error is silently ignored
try {
  const result = await myStep( input );
} catch ( error ) {
  console.log( 'Step failed' );  // Swallowed!
  return { success: false };
}

Pattern 2: FatalError Wrapping

// WRONG: Turns retryable errors into fatal errors
try {
  const result = await myStep( input );
} catch ( error ) {
  throw new FatalError( error.message );  // Prevents retries!
}

Pattern 3: Re-throwing Generic Errors

// WRONG: Loses error context and may affect retry behavior
try {
  const result = await myStep( input );
} catch ( error ) {
  throw new Error( `Step failed: ${error.message}` );
}

Solution

Let failures propagate naturally. Remove try-catch blocks around step calls and let the Output SDK handle errors:

Before (Wrong)

export default workflow( {
  fn: async input => {
    try {
      const data = await fetchDataStep( input );
      const result = await processDataStep( data );
      return result;
    } catch ( error ) {
      throw new FatalError( error.message );
    }
  }
} );

After (Correct)

export default workflow( {
  fn: async input => {
    const data = await fetchDataStep( input );
    const result = await processDataStep( data );
    return result;
  }
} );

When Try-Catch IS Appropriate

There are limited cases where catching errors in workflows is valid:

1. Optional/Fallback Steps

When a step failure should trigger an alternative path:

export default workflow( {
  fn: async input => {
    const data = await ( async () => {
      try {
        return await fetchFromPrimarySource( input );
      } catch {
        return await fetchFromSecondarySource( input );
      }
    } )();
    return await processData( data );
  }
} );

For readability, you can extract the fallback logic into a named helper function instead of using an IIFE:

const fetchWithFallback = async input => {
  try {
    return await fetchFromPrimarySource( input );
  } catch {
    return await fetchFromSecondarySource( input );
  }
};

export default workflow( {
  fn: async input => {
    const data = await fetchWithFallback( input );
    return await processData( data );
  }
} );

2. Aggregate Results with Partial Failures

When processing multiple items where some may fail:

export default workflow( {
  fn: async input => {
    const results = [];
    for ( const item of input.items ) {
      try {
        const result = await processItem( item );
        results.push( { item, result, success: true } );
      } catch ( error ) {
        results.push( { item, error: error.message, success: false } );
      }
    }
    return results;  // Contains both successes and failures
  }
} );

Note: Even in these cases, be careful not to swallow errors that should cause the whole workflow to fail.

Finding Try-Catch Around Steps

Search for the pattern:

# Find try blocks in workflow files
grep -rn "try {" src/workflows/

# Look for FatalError usage
grep -rn "FatalError" src/workflows/

Then review each match to see if it's wrapping step calls.

How Retries Work

When you DON'T catch errors:

1. Step throws an error
2. Output SDK receives the error
3. SDK checks retry policy (configured per step)
4. If retries remain, step is re-executed
5. If retries exhausted, workflow fails with full error context

When you DO catch errors:

1. Step throws an error
2. Your catch block handles it
3. Output SDK never sees the original error
4. Retry logic is bypassed
5. You control what happens (often incorrectly)

Configuring Retry Behavior

Instead of try-catch, configure retry policies on steps:

export const fetchData = step( {
  name: 'fetchData',
  retry: {
    maxAttempts: 3,
    initialInterval: '1s',
    maxInterval: '30s',
    backoffCoefficient: 2
  },
  fn: async input => {
    // If this fails, it will be retried according to policy
    return await callApi( input );
  }
} );

Using FatalError Correctly

FatalError is for errors that should NEVER be retried:

export const validateInput = step( {
  name: 'validateInput',
  fn: async input => {
    if ( !input.userId ) {
      // This will never succeed on retry
      throw new FatalError( 'userId is required' );
    }
    return input;
  }
} );

Do NOT use FatalError to wrap other errors unless you're certain they shouldn't retry.

Verification

After removing try-catch:

1. Test normal operation: npx output workflow run <name> --input '<valid-input>'
2. Test failure scenarios: Use input that causes step failures
3. Check retry behavior: Look for retry attempts in npx output workflow debug <id>

Related Issues

• For configuring retry policies, see step definition documentation
• For handling expected failures gracefully, consider using conditional logic instead of try-catch