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    5.3.3 • Public • Published

    @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




    npm i @arpinum/log

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    • michaelborde
    • arpinum
    • emeric.gaichet