chubbyts-log-types

Description

Log (logger) types, PSR-3 inspired.

The package ships only types and a tiny createLogger helper, so libraries can depend on a logger contract without depending on a concrete logging implementation.

Requirements

• node: >=22

Installation

Through NPM as @chubbyts/chubbyts-log-types.

npm i @chubbyts/chubbyts-log-types@^3.4.1

Usage

Types

import type {
  Context,
  LogFn,
  Logger,
  LogLevel,
  NamedLogFn,
} from '@chubbyts/chubbyts-log-types/log';

type LogLevel =
  | 'emergency'
  | 'alert'
  | 'critical'
  | 'error'
  | 'warning'
  | 'notice'
  | 'info'
  | 'debug';

type Context = Record<string, unknown>;

type LogFn = (level: LogLevel, message: string, context: Context) => void;
type NamedLogFn = (message: string, context: Context) => void;

// one NamedLogFn per LogLevel, plus the generic log function
type Logger = Record<LogLevel, NamedLogFn> & { log: LogFn };

Create a logger

createLogger takes a single LogFn and derives all level-specific methods from it.

import { createLogger } from '@chubbyts/chubbyts-log-types/log';

const logger = createLogger((level, message, context) => {
  const datetime = new Date().toISOString();

  console.log(JSON.stringify({ datetime, level, message, context }));
});

logger.info('User logged in', { userId: 'a1b2c3' });
logger.error('Payment failed', { orderId: 42, reason: 'card declined' });
logger.log('warning', 'Disk space low', { freeBytes: 1_024 });

Null logger

Without an argument createLogger returns a logger that discards every message, which is handy as a default or within tests.

import { createLogger } from '@chubbyts/chubbyts-log-types/log';

const logger = createLogger();

logger.debug('This goes nowhere', {});

Depend on the type

Accept a Logger instead of a concrete implementation.

import type { Logger } from '@chubbyts/chubbyts-log-types/log';
import { createLogger } from '@chubbyts/chubbyts-log-types/log';

export const createUserService = (logger: Logger = createLogger()) => ({
  delete: (id: string) => {
    logger.notice('User deleted', { id });
  },
});

Filter by level

import type { LogFn, LogLevel } from '@chubbyts/chubbyts-log-types/log';
import { createLogger } from '@chubbyts/chubbyts-log-types/log';

// ordered from most to least severe
const levels: Array<LogLevel> = [
  'emergency',
  'alert',
  'critical',
  'error',
  'warning',
  'notice',
  'info',
  'debug',
];

const createMinLevelLogFn =
  (minLevel: LogLevel, log: LogFn): LogFn =>
  (level, message, context) => {
    if (levels.indexOf(level) <= levels.indexOf(minLevel)) {
      log(level, message, context);
    }
  };

const logger = createLogger(
  createMinLevelLogFn('warning', (level, message, context) => {
    console.log(level, message, context);
  }),
);

logger.error('Shown', {});
logger.info('Suppressed', {});

Copyright

2026 Dominik Zogg