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Module Logger Pattern ​

Problem ​

Log entries from different modules are mixed in the output, making it hard to filter by origin. Each module should create its own logger with a fixed namespace so entries can be filtered without additional context.

Solution ​

Use createLogger(name) to create a fixed-namespace logger for each module and export it as a named constant.

ts
import { createLogger } from '@vielzeug/rune';

export const log = {
  api: createLogger('api'),
  auth: createLogger('auth'),
  db: createLogger('db'),
};

log.api.info('GET /users');
log.auth.warn('token expiring');

Pitfalls ​

  • Using the same namespace string in two different modules makes their log entries indistinguishable. Use hierarchical namespaces (e.g., app:orders:service) to ensure uniqueness.
  • Creating the logger at module load time means its namespace and bindings are fixed for that module instance. Prefer request-scoped child loggers when fields vary per request.
  • Structured context is first-argument only: use logger.info({ userId }, 'event'). String-first calls accept only the message.