Advanced Node.js

Chapter 12: Error Handling and Logging

12.1 Error Handling Patterns

Proper error handling ensures applications fail gracefully and provide useful information for debugging.

// Custom error class
class AppError extends Error {
    constructor(message, statusCode) {
        super(message);
        this.statusCode = statusCode;
        this.isOperational = true;
        Error.captureStackTrace(this, this.constructor);
    }
}

// Async error wrapper
const asyncHandler = (fn) => (req, res, next) => {
    Promise.resolve(fn(req, res, next)).catch(next);
};

// Global error handler
app.use((err, req, res, next) => {
    err.statusCode = err.statusCode || 500;
    err.status = err.status || 'error';
    
    if (process.env.NODE_ENV === 'development') {
        res.status(err.statusCode).json({
            status: err.status,
            error: err,
            message: err.message,
            stack: err.stack
        });
    } else {
        res.status(err.statusCode).json({
            status: err.status,
            message: err.message
        });
    }
});

12.2 Logging Strategies

// Winston logger
const winston = require('winston');

const logger = winston.createLogger({
    level: 'info',
    format: winston.format.json(),
    transports: [
        new winston.transports.File({ filename: 'error.log', level: 'error' }),
        new winston.transports.File({ filename: 'combined.log' })
    ]
});

if (process.env.NODE_ENV !== 'production') {
    logger.add(new winston.transports.Console({
        format: winston.format.simple()
    }));
}

// Usage
logger.info('User logged in', { userId: 123 });
logger.error('Database error', { error: err });

12.3 Structured Logging

// Pino logger (faster)
const pino = require('pino');
const logger = pino({
    level: 'info',
    transport: {
        target: 'pino-pretty'
    }
});

logger.info({ userId: 123, action: 'login' }, 'User logged in');
logger.error({ err }, 'Error occurred');