Logging Basics

8 examples to get you started with Logging for Node.js backends - 6 basic and 2 intermediate.

Prerequisites

npm install pino
npm install -D pino-pretty typescript@5.6 tsx

Production services on Node 24.18.0 should emit structured JSON to stdout - aggregators (Datadog, Loki, CloudWatch) parse one object per line.

Basic Examples

1. Structured JSON Instead of String Concatenation

Machines parse fields; humans grep level and requestId.

import pino from "pino";
 
const logger = pino({ level: "info" });
 
logger.info({ userId: "u_123", action: "login_success" }, "user logged in");
// {"level":30,"userId":"u_123","action":"login_success","msg":"user logged in",...}

• First argument is a context object; second is a short human message.
• String templates like `User ${id} logged in` lose searchable fields.
• level 30 is info in Pino's numeric mapping.

Related: pino - child loggers and redaction

2. Log Levels Mean Something

Pick the level that matches operator response, not developer mood.

logger.fatal({ err }, "database unreachable at boot");
logger.error({ err, orderId }, "payment capture failed");
logger.warn({ retryCount: 3 }, "downstream timeout, retrying");
logger.info({ requestId }, "request completed");
logger.debug({ query }, "sql executed");

• error - needs investigation or user impact.
• warn - degraded but recovering (retries, fallbacks).
• info - normal business and request lifecycle events.
• debug - development only or sampled in production.

Related: Logging Best Practices - prod log level policy

3. Log Errors with the err Key

Pino's standard serializer captures stack traces.

try {
  await chargeCard(orderId);
} catch (err) {
  logger.error({ err, orderId }, "charge failed");
}

• { err } triggers pino.stdSerializers.err - stack and type preserved.
• logger.error(err) without object wrapper loses field structure.
• Map to HTTP 5xx after logging - log first, then respond generically.

Related: Error Response Standards - client vs log detail

4. Ban console.log in Application Code

Unstructured lines break JSON-only log pipelines.

// eslint no-console: error
import pino from "pino";
const log = pino();
log.info({ event: "worker_started" });

• console.log bypasses level filters and redaction.
• ESLint no-console in src/ with exception for CLI scripts.
• Tests can use pino.destination({ sync: true }) for capture.

Related: Logging with Pino on Fastify - framework integration

5. Include Request Metadata on Every HTTP Log

Method, path, status, and duration power SLO dashboards.

logger.info({
  event: "request_complete",
  method: "GET",
  path: "/users",
  statusCode: 200,
  durationMs: 42,
  requestId: "req_abc",
});

• Consistent field names across services (requestId, not reqId in one app and rid in another).
• Duration from reply.elapsedTime (Fastify) or middleware timing (Express).
• Health checks can be sampled or excluded to reduce noise.

Related: Request Correlation IDs - x-request-id

6. One Logger Instance Per Process

Create at module scope; avoid pino() per request.

// src/logger.ts
import pino from "pino";
 
export const logger = pino({
  level: process.env.LOG_LEVEL ?? "info",
  base: { service: "orders-api", version: process.env.APP_VERSION },
});

• base fields appear on every line - service name for multi-tenant log indexes.
• Child loggers add per-request fields without reconfiguring the root.
• Pass logger to workers via import, not global mutation.

Related: pino - configuration options

Intermediate Examples

7. Child Logger for Request Context

Bind requestId once; all downstream logs inherit it.

const child = logger.child({ requestId: "req_abc", tenantId: "t_1" });
child.info({ action: "fetch_order" });
child.info({ action: "send_receipt" });
// both lines include requestId and tenantId

• Create child in HTTP middleware or Fastify onRequest hook.
• After auth, req.log = req.log.child({ userId: user.id }).
• Child loggers are cheap - prefer over manual spread on every call.

Related: AsyncLocalStorage for Context - non-HTTP workers

8. Redact Sensitive Paths

Keep passwords and tokens out of log storage.

const logger = pino({
  redact: {
    paths: ["req.headers.authorization", "req.body.password", "email"],
    censor: "[REDACTED]",
  },
});

• Redaction runs at serialize time - safer than hoping developers remember.
• List paths in a security review checklist.
• GDPR and PCI often require email/phone redaction or hashing in logs.

Related: PII Redaction & Compliance - retention policies

Stack versions: This page was written for Node.js 24.18.0 (Active LTS), npm 10+, TypeScript 5.6+, Express 5, Fastify 5, and NestJS 11.