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    Mag is the streaming logger for NodeJS


    $ npm install mag --save

    Use cases

    Everyday use cases

    If you have something to show in the terminal, use the mag as well as you used console.log before.

    var logger = require('mag')();
'my great application is running!');
    logger.debug('process pid is %s',;
    //01:27:36.427 <INFO> my great application is running!
    //01:27:36.429 <DEBUG> process pid is 29860

    You get well formatted message with timestamp.

    If you need to visually separate the messages from different sources, use the namespace of mag.

    var mag = require('mag');
    var logger = mag('my-app');
    var libLogger = mag('my-lib');
'my great application is running');
    libLogger.debug('my library is running too');
    //22:36:24.245 [my-app] <INFO> my great application is running
    //22:36:24.246 [my-lib] <DEBUG> my library is running too

    For application developers

    If you're thinking about formatting the output messages of your application, just require mag-hub before all mag requires.

    mag-hub is passthrough stream. If you require mag-hub then all log objects will be written to this stream. You can read from this stream and make any transformation with your messages before writing them to stdout.

    var hub = require('mag-hub');
    // Formatters
    var info = require('mag-process-info');
    var format = require('mag-format-message');
    var colored = require('mag-colored-output');
    var myCustomFormatter = require('./my-custom-formatter.js');

    More information are in mag-hub module.

    For module developers

    If you're developing a module and you have something to write to the log, just use the mag.

    var mag = require('mag');
    var logger = mag('my-module');
    var env = process.env.NODE_ENV || 'development';
'module is running in %s environment', env);
    myModule.on('heartbeat', function(){
      logger.debug('heartbeat of module');
    myModule.on('error', function(){
      logger.critical(new Error('game is over'));

    You must not to worry about the output message format. (In other loggers you have to think about the message format even if you develop a module - it is bad practice)

    If users of your module want to format log of the module they can require mag-hub in their application and format logs as they want. See previous section for app developers for more information.

    Warning: mag-hub is designed for use only at the application leyer, do not require it into your modules distributed via npm.



    • You do not have to configure the output if you develop a module
    • You can do anything with the output if you develop an application

    How does it work?

    Specification of internal messages format can be found here:


    You can find examples of using mag logger in this reposiory: mag-examples.

    There are following branches:

    • simple - simplest replacement of console
    • module - module using mag as logger
    • app - example of application that uses the module above
    • app-formatted-output - mag-hub, log levels, and collored output (full example of mag power)


    A brief interpretation of The Twelve-Factor App - Logs section:

    • Log is the stream of time-ordered events.
    • App never concerns itself with routing or storage of its output stream.
    • App should not attempt to write to or manage logfiles.
    • App should write its event stream, unbuffered, to stdout.




    npm i mag

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