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Preserve error context

When handling errors, always ensure the original error context is preserved and properly surfaced. Error information should never be silently swallowed in try/catch blocks, as this makes debugging extremely difficult and can lead to unexpected system behavior.

raw .md Error Handling JavaScript

There are two recommended approaches to preserving error context:

Use the standard error.cause property to maintain error chains:

try {
  // Original operation
  const result = func(error, reply.request, reply);
  // Process result...
} catch (err) {
  // Preserve original error context
  if (!Object.prototype.hasOwnProperty.call(err, 'cause')) {
    err.cause = error; // Link the original error as the cause
  } else {
    // Log when unable to set cause to avoid losing context
    logger.warn({
      err: error,
      parentError: err,
      message: 'Original error cannot be linked as cause'
    });
  }
  
  // Propagate the error with context preserved
  throw err;
}

In asynchronous code, ensure proper promise rejection handling:

// BAD: Double resolution if error occurs
sget(options, (err, response, body) => {
  if (err) reject(err)
  resolve({ response, body }) // Still runs after reject!
})

// GOOD: Return after rejection to prevent double resolution
sget(options, (err, response, body) => {
  if (err) {
    reject(err)
    return // Important! Prevents executing the resolve
  }
  resolve({ response, body })
})

Remember that proper error handling includes validation of your error conditions themselves. Be careful with falsy checks that might incorrectly handle empty strings or zero values as error conditions.