Summary

This is a lightweight library to handle logs in an application. It is written in Typescript but can be used in a JS project.

Usage

Simple usage:

import { logger } from "rauricoste-logger";

logger.info("hello world");
// 2025/10/17 11:31:31.508 INFO _ hello world

Log levels

Default log level is INFO

import { logger } from "rauricoste-logger";

logger.debug("hello world");
// not working
logger.info("hello world");
// 2025/10/17 11:31:31.508 INFO _ hello world

There are 5 default log levels:

import { logger, LoggerLevel } from "rauricoste-logger";

logger.setLevel(LoggerLevel.DEBUG);

logger.debug("hello world");
logger.info("hello world");
logger.warn("hello world");
logger.error("hello world");
logger.fatal("hello world");
// 2025/10/17 11:31:31.507 DEBUG _ hello world
// 2025/10/17 11:31:31.508 INFO _ hello world
// 2025/10/17 11:31:31.508 WARN _ hello world
// 2025/10/17 11:31:31.508 ERROR _ hello world
// 2025/10/17 11:31:31.508 FATAL _ hello world

It is possible to log at a custom log level:

logger.log(23, "special log level");
// 11:24:56.431 WARN _ special log level

Log level are actually mapped to a number:

const LoggerLevel = {
  DEBUG: 10,
  INFO: 20,
  WARN: 30,
  ERROR: 40,
  FATAL: 50,
};

The log level of a logger can be set dynamically:

import { logger, LoggerLevel } from "rauricoste-logger";

logger.setLevel(LoggerLevel.DEBUG);
logger.debug("hello world");
// nothing is logged

logger.setLevel(LoggerLevel.WARN);
logger.debug("hello world");
// 2025/10/17 11:36:58.671 DEBUG _ hello world

Logger hierarchy

Loggers can have children that inherit the log levels and appenders.

import { logger, LoggerLevel } from "rauricoste-logger";

const childLogger = logger.getLogger("child");
childLogger.warn("test");
// 2025/10/17 11:42:46.365 WARN _.child test

logger.setLevel(LoggerLevel.WARN);
console.log(logger.level);
// 30
console.log(childLogger.level);
// 30

logger.setLevel(LoggerLevel.ERROR);
console.log(logger.level);
// 40
console.log(childLogger.level);
// 40

Child loggers are linked to their name:

import { logger } from "rauricoste-logger";

const childLogger = logger.getLogger("child");
const childLogger2 = logger.getLogger("child");
console.log(childLogger === childLogger2);
// true

Appenders

By default, the console appender is configured but it is possible to remove or add any appender.

An appender is defined by:

type Appender = (logger: Logger, level: LoggerLevel, ...args: any[]) => void;

You can change the appenders:

import { type Appender, Logger, logger, LoggerLevel } from "rauricoste-logger";

const dumbAppender: Appender = (
  logger: Logger,
  level: LoggerLevel,
  ...args
) => {
  console.log(logger.name, level, ...args);
};
logger.appenders = [dumbAppender];

logger.info("hello world");
// _ 20 hello world