@lib-stack/logger

A lightweight logger with configurable log levels, hierarchical child loggers, and pluggable output backends.

Install

pnpm add @lib-stack/logger

Usage

import { createLogger, logger } from '@lib-stack/logger'

// Use the pre-built default logger
logger.setLevel('info')
logger.info('Hello world') // [2025-04-11 10:00:00] [INFO] [default] - Hello world
logger.debug('Hidden') // (no output, debug < info)

// Create a named logger
const app = createLogger({ name: 'app' })
app.setLevel('warn')
app.warn('Something is off')
app.error('Something broke')

Child Loggers

const parent = createLogger({ name: 'server' })
parent.setLevel('info')

const child = parent.get('http')
child.setLevel('debug')

child.debug('Request received') // [2025-04-11 10:00:00] [DEBUG] [http] - Request received
child.parent() // => parent logger
parent.getAll() // => [child]

Custom Log Backend

import type { LogApi } from '@lib-stack/logger'
import { createLogger } from '@lib-stack/logger'

const customApi: LogApi = {
  trace: (...args) => sendToServer('trace', args),
  debug: (...args) => sendToServer('debug', args),
  info: (...args) => sendToServer('info', args),
  warn: (...args) => sendToServer('warn', args),
  error: (...args) => sendToServer('error', args),
  fatal: (...args) => sendToServer('fatal', args),
}

const log = createLogger({ name: 'remote', logApi: customApi })
log.setLevel('error')
log.error('Critical failure') // sent to server

Log Levels

From lowest to highest priority:

| Level | Value | Description | |-------|-------|-------------| | all | 0 | Enable all log types | | trace | 0 | Detailed tracing | | debug | 1 | Debug information | | info | 2 | General information | | warn | 3 | Warnings | | error | 4 | Errors | | fatal | 5 | Fatal errors | | off | 6 | Disable all logging |

A log call is only emitted when its level value is >= the logger's current level.

API

createLogger(options?): Logger

Create a new logger instance.

• options.name - Logger name, shown in output (default: 'default')
• options.logApi - Custom output backend (default: defaultLogApi using console)
• options.parent - Parent logger reference

Logger

| Method | Description | |--------|-------------| | trace(...args) | Log at trace level | | debug(...args) | Log at debug level | | info(...args) | Log at info level | | warn(...args) | Log at warn level | | error(...args) | Log at error level | | fatal(...args) | Log at fatal level | | setLevel(level) | Set the minimum log level | | getLevel() | Get the current log level | | get(name?, options?) | Get or create a child logger | | getAll() | List all child loggers | | parent() | Get the parent logger |

logger

A pre-built default logger instance (level defaults to 'off').

License

MIT