How do you implement logging in a Node.js application?
Why Interviewers Ask This
This question targets practical, hands-on experience with Node.js. Interviewers want to see if you've worked with these concepts in real projects, not just read about them. Strong answers include concrete examples.
Answer
Effective logging is critical for debugging and monitoring Node.js production applications. console.log() is acceptable for development but insufficient for production. Production logging requirements: structured logs (JSON format for log aggregation), log levels (error, warn, info, debug), timestamps, contextual data, and transport options (file, stdout, external services). Libraries: (1) Winston — most popular, supports multiple transports, log rotation, custom formatters: const logger = winston.createLogger({ level: "info", format: winston.format.json(), transports: [new winston.transports.Console(), new winston.transports.File({ filename: "error.log", level: "error" })] });; (2) Pino — extremely fast (10x faster than Winston due to minimal sync operations), JSON output by default, used by Fastify; (3) Morgan — HTTP request logger middleware for Express. Best practices: log at the appropriate level, never log sensitive data (passwords, tokens, PII), use correlation IDs to trace requests across services, and send logs to centralized systems (Datadog, ELK Stack, CloudWatch) in production.
Pro Tip
This topic has Node.js-specific nuances that differ from general programming. Highlighting those nuances in your answer shows expertise rather than generic knowledge.