Simple module to log on stdout or stderr

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@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 import default logger and start yelling messages:
import { logger } from "@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:
import { createLogger } from "@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 - ARP_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) - ARP_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 ARP_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:
import { createLogger } from "@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