@twin-digital/logger-lib

Generic logging interface and context management for TypeScript applications.

Overview

This library provides a common Logger interface and contextual logger pattern using Node.js AsyncLocalStorage. Write code that logs via getLogger() without coupling to a specific logging implementation.

Default Implementations

consoleLogger

Simple console-based logger for development and testing.

import { consoleLogger } from '@twin-digital/logger-lib'

consoleLogger.info('Application started')
consoleLogger.error('Something went wrong', { error })

noopLogger

Silent logger that discards all log statements. Useful for testing or disabling logs.

Contextual Logging

Why?

In serverless and async environments (AWS Lambda, HTTP servers), you need logger instances with request-specific context (requestId, userId, correlationId) without passing loggers through every function call.

When?

Use contextual logging when:

• Building AWS Lambda functions with per-request context
• Writing middleware that needs to inject contextual information
• Testing code that depends on loggers without complex dependency injection

How?

Set logger context (middleware pattern):

import { setLogger } from '@twin-digital/logger-lib'

// In middleware/setup code
const logger = createLogger({ serviceName: 'my-service' })
logger.appendKeys({ requestId, userId })
setLogger(logger)

Get logger anywhere in your code:

import { getLogger } from '@twin-digital/logger-lib'

async function processOrder(orderId: string) {
  const logger = getLogger() // Gets contextual logger automatically
  logger.info('Processing order', { orderId })

  await validateOrder(orderId) // Logger context maintained across async calls

  logger.info('Order processed')
}

Wrap operations with scoped context:

import { runWithLogger } from '@twin-digital/logger-lib'

// For testing or scoped operations
await runWithLogger(mockLogger, async () => {
  await myFunction() // Uses mockLogger via getLogger()
})
// Context automatically reverts after callback

Context Isolation

Logger context is automatically isolated between:

• Concurrent AWS Lambda invocations
• Concurrent HTTP requests
• Parallel async operations

No explicit cleanup required - AsyncLocalStorage handles it.

Fallback Behavior

getLogger() returns a console-based logger when no context is set, ensuring your code always works even without explicit logger setup.