Simple module to log on stdout or stderr


105.3.23 months ago5 years agoMinified + gzip package size for @arpinum/log in KB


@arpinum/log Build Status

We are drowning in information but starved for knowledge.
John Naisbitt

@arpinum/log is a simple module to log on stdout or stderr.


npm install @arpinum/log --save

Default logger

Just require default logger and start yelling messages:

const { logger } = require("@arpinum/log");

logger.info("Something happened");

Which outputs :

2017-01-30T09:15:04.821Z - info: [default] Something happened

Logging methods

Available methods are:

  • debug
  • info
  • warn
  • error

Each level uses corresponding method on console global object and fallback to console.log if missing for runtime environment.

Custom logger

You can create a fine tuned logger:

const { createLogger } = require("@arpinum/log");

const logger = createLogger({ level: "error" });
logger.info("Something happened");
logger.error("Some error");

Which outputs :

2017-01-30T09:23:33.417Z - error: [default] Some error


You can pass those options during logger creation:

  • level
    • minimum logging level amongst all, debug, info, warn, error, off
    • default is info
    • LOG_LEVEL env var may be used to set level
  • category
    • the category displayed in message, useful to filter logs
    • default is default
  • fileName
    • a category can be created from a base name without extension of a file
  • filter
    • a regex to filter matching categories
    • default is .* (open bar)
    • LOG_FILTER env var may be used to set filter
  • getDateString
    • a function to get a formatted date
    • default function returns new Date().toISOString()
    • provide null if you do not want a date at all
  • getLogInputs
    • a function to get inputs given to console methods
    • used to format message as you want
    • see Customize message below

Filtering logs

If you have multiple logger instances with various categories, you can filter logs using filter options or LOG_FILTER env var.


// program.js
const mainLogger = createLogger({ category: "main" });
const serviceLogger = createLogger({ category: "service" });

mainLogger.info("Application started");
serviceLogger.info("Doing some stuff");

May be run with LOG_FILTER=serv node program.js to output:

2017-01-30T09:32:31.351Z - info: [service] Doing some stuff

About category:

File name usage:

const { createLogger } = require("@arpinum/log");

const logger = createLogger({ fileName: __filename });
logger.info("Something happened");

Which outputs :

2017-01-30T09:32:31.351Z - info: [MySuperClass] Something happened

Customize message

getLogInputs will be called for each log with an object containing:

  • date: the current date string
  • category: the configured category
  • level: the logger level
  • args: all the provided args


const logger = createLogger({
  getLogInputs: ({ date, category, level, args }) => [

logger.info("My", "message");

// 2019-11-19T16:45:58.419Z|default|info My message



If you find any bugs or have a feature request, please open an issue on github!

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