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Logging in Node.js

Logging is essential for monitoring, debugging, and maintaining Node.js applications. Good logs provide visibility into what the system is doing and help identify issues quickly.

Best Practices

  • Log Levels: Use different levels like info, warn, error, and debug.
  • Structured Logging: Log in JSON format to make it easy for machines to parse and analyze.
  • Don’t use console.log: Avoid it in production as it is synchronous and lacks features.
  • Sensitive Data: Never log passwords, tokens, or PII.

1. Winston

A flexible and feature-rich logging library with support for multiple transports (console, file, database).

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(),
  }));
}


logger.info('Application started');

2. Pino

A very low-overhead logging library that focuses on speed and structured output.

const logger = require('pino')();


logger.info('hello world');
logger.error({ err: new Error('an error') }, 'something went wrong');

Log Monitoring

Consider using external tools to aggregate and analyze your logs:

  • ELK Stack (Elasticsearch, Logstash, Kibana)
  • Datadog
  • Sentry (for error tracking)
  • Papertrail