Node.js Centralized Logging & Error Handling

A comprehensive logging and error handling module for Node.js microservices using Winston.

Features

• Standardized Error Handling: ApiError class with centralized error codes
• Multi-transport Logging: Console and file logging with Winston
• HTTP Request Tracking: Middleware for logging requests with performance metrics
• Environment-aware Formatting: Colorized for development, JSON for production
• Structured Logging: Consistent metadata across all log entries

Installation

npm install

Usage

Basic Setup

const express = require('express');
const { logger, errorHandler, requestLogger } = require('./path-to-module');

const app = express();

// Apply request logger as early as possible
app.use(requestLogger);

// Your routes and other middleware here

// Apply error handler as the last middleware
app.use(errorHandler);

app.listen(3000, () => {
  logger.info('Server started on port 3000');
});

Logging

const { logger } = require('./path-to-module');

// Different log levels
logger.error('Critical application error', { details: err });
logger.warn('Warning condition', { source: 'database' });
logger.info('Informational message');
logger.http('HTTP-specific information');
logger.debug('Debugging information');

// With metadata
logger.info('User logged in', {
  userId: user.id,
  email: user.email,
  timestamp: new Date()
});

Error Handling

const { ApiError } = require('./path-to-module');

// Using error factory methods
app.get('/users/:id', (req, res, next) => {
  const user = findUser(req.params.id);
  
  if (!user) {
    return next(ApiError.notFound('User not found'));
  }
  
  if (!canAccessUser(req.user, user)) {
    return next(ApiError.forbidden('You cannot access this user'));
  }
  
  res.json(user);
});

// Handling validation errors
app.post('/users', (req, res, next) => {
  const { name, email } = req.body;
  const errors = {};
  
  if (!name) errors.name = 'Name is required';
  if (!email) errors.email = 'Email is required';
  
  if (Object.keys(errors).length > 0) {
    return next(ApiError.validationError('Validation failed', errors));
  }
  
  // Create user...
  res.status(201).json(user);
});

// Catching and converting other errors
app.get('/data', async (req, res, next) => {
  try {
    const data = await fetchData();
    res.json(data);
  } catch (err) {
    // Convert to API error
    next(ApiError.internal('Failed to fetch data', {}, err));
  }
});

Example Server

Run the example server to see the logger in action:

npm start

Then visit:

• http://localhost:3000/ - Basic route
• http://localhost:3000/log-levels - See different log levels
• http://localhost:3000/error - Triggers a generic error
• http://localhost:3000/api-error - Triggers an API error
• http://localhost:3000/not-found - 404 error
• POST http://localhost:3000/users - Test validation errors

Environment Variables

• NODE_ENV: Set to 'production' for production-optimized logging
• LOG_LEVEL: Override default log level (default: 'debug' in dev, 'info' in prod)
• SERVICE_NAME: Name of your service (included in logs)
• LOG_DIR: Directory for log files (default: 'logs')