How to Handle Async Errors in Node.js Effectively

Dealing with asynchronous errors in Node.js can be tricky. One small oversight in error handling can bring down your entire application. Let’s explore some battle-tested patterns and best practices to handle async errors effectively.

Understanding Async Error Patterns

The asynchronous nature of Node.js means errors can occur in various contexts - Promises, async/await, callbacks, and event emitters. Each requires a specific approach to handle errors gracefully.

Key Strategies for Robust Error Handling

1. Using try-catch with async/await

async function fetchUserData(userId) {
  try {
    const user = await database.users.findById(userId);
    return user;
  } catch (error) {
    logger.error('Failed to fetch user:', error);
    throw new CustomError('UserFetchError', error.message);
  }
}

2. Implementing Global Error Handlers

process.on('unhandledRejection', (reason, promise) => {
  console.error('Unhandled Rejection:', reason);
  // Proper error logging and handling
});

process.on('uncaughtException', (error) => {
  console.error('Uncaught Exception:', error);
  // Graceful shutdown procedures
  process.exit(1);
});

3. Creating Error Boundaries

class ErrorBoundary {
  async execute(fn) {
    try {
      return await fn();
    } catch (error) {
      this.handleError(error);
      throw error;
    }
  }

  handleError(error) {
    // Custom error handling logic
    logger.error(error);
    metrics.recordError(error);
  }
}

Best Practices

1. Always use async/await with try-catch
2. Create custom error classes for better error handling
3. Implement proper logging and monitoring
4. Use middleware for REST API error handling
5. Never ignore errors in promises or callbacks

Common Pitfalls to Avoid

• Forgetting to handle rejected promises
• Ignoring errors in event emitters
• Not implementing proper cleanup in catch blocks
• Missing error types in TypeScript implementations

Advanced Error Handling Patterns

// Error handler middleware for Express
app.use((error, req, res, next) => {
  logger.error(error);
  res.status(error.status || 500).json({
    error: {
      message: error.message,
      code: error.code
    }
  });
});

Remember, effective error handling is not just about preventing crashes - it’s about maintaining system reliability and providing a great user experience.