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This is a conversion of the log4js framework to work with node. I started out just stripping out the browser-specific code and tidying up some of the javascript to work better in node. It grew from there. Although it's got a similar name to the Java library log4j, thinking that it will behave the same way will only bring you sorrow and confusion.

The full documentation is available here.

There have been a few changes between log4js 1.x and 2.x (and 0.x too). You should probably read this migration guide if things aren't working.

Out of the box it supports the following features:

  • coloured console logging to stdout or stderr
  • file appender, with configurable log rolling based on file size or date
  • SMTP appender
  • GELF appender
  • Loggly appender
  • Logstash (UDP and HTTP) appender
  • logFaces (UDP and HTTP) appender
  • multiprocess appender (useful when you've got multiple servers)
  • a logger for connect/express servers
  • configurable log message layout/patterns
  • different log levels for different log categories (make some parts of your app log as DEBUG, others only ERRORS, etc.)

Getting help

Having problems? Jump on the slack channel, or create an issue. If you want to help out with the development, the slack channel is a good place to go as well.


npm install log4js


Minimalist version:

var log4js = require('log4js');
var logger = log4js.getLogger();
logger.level = 'debug';
logger.debug("Some debug messages");

By default, log4js will not output any logs (so that it can safely be used in libraries). The level for the default category is set to OFF. To enable logs, set the level (as in the example). This will then output to stdout with the coloured layout (thanks to masylum), so for the above you would see:

[2010-01-17 11:43:37.987] [DEBUG] [default] - Some debug messages

See example.js for a full example, but here's a snippet (also in examples/fromreadme.js):

const log4js = require('log4js');
  appenders: { cheese: { type: 'file', filename: 'cheese.log' } },
  categories: { default: { appenders: ['cheese'], level: 'error' } }
const logger = log4js.getLogger('cheese');
logger.trace('Entering cheese testing');
logger.debug('Got cheese.');'Cheese is Gouda.');
logger.warn('Cheese is quite smelly.');
logger.error('Cheese is too ripe!');
logger.fatal('Cheese was breeding ground for listeria.');

Output (in cheese.log):

[2010-01-17 11:43:37.987] [ERROR] cheese - Cheese is too ripe!
[2010-01-17 11:43:37.990] [FATAL] cheese - Cheese was breeding ground for listeria.

Note for library makers

If you're writing a library and would like to include support for log4js, without introducing a dependency headache for your users, take a look at log4js-api.


Available here.

There's also an example application.


import { configure, getLogger } from './log4js';
const logger = getLogger();
logger.level = 'debug';
logger.debug("Some debug messages");
    appenders: { cheese: { type: 'file', filename: 'cheese.log' } },
    categories: { default: { appenders: ['cheese'], level: 'error' } }


We're always looking for people to help out. Jump on slack and discuss what you want to do. Also, take a look at the rules before submitting a pull request.


The original log4js was distributed under the Apache 2.0 License, and so is this. I've tried to keep the original copyright and author credits in place, except in sections that I have rewritten extensively.