A port of log4js to node.js
Latest commit 2e3cb97 Mar 27, 2017 @nomiddlename committed on GitHub Merge pull request #465 from jpstotz/master
bugfix for issue #457


log4js-node Build Status


This is a conversion of the log4js framework to work with node. I've mainly stripped out the browser-specific code and tidied up some of the javascript.

Out of the box it supports the following features:

  • coloured console logging to stdout or stderr
  • replacement of node's console.log functions (optional)
  • file appender, with configurable log rolling based on file size or date
  • SMTP appender
  • GELF appender
  • Loggly appender
  • Logstash UDP appender
  • logFaces appender
  • multiprocess appender (useful when you've got worker processes)
  • 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.)

Important changes in 1.0

The default appender has been changed from console to stdout - this alleviates a memory problem that happens when logging using console. If you're using log4js in a browser (via browserify), then you'll probably need to explicitly configure log4js to use the console appender now (unless browserify handles process.stdout).

I'm also trying to move away from vows for the tests, and use tape instead. New tests should be added to test/tape, not the vows ones.

log4js also no longer supports node versions below 0.12.x.

NOTE: from log4js 0.5 onwards you'll need to explicitly enable replacement of node's console.log functions. Do this either by calling log4js.replaceConsole() or configuring with an object or json file like this:

  appenders: [
    { type: "console" }
  replaceConsole: true


npm install log4js


Minimalist version:

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

By default, log4js outputs 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 fromreadme.js):

var log4js = require('log4js');
//console log is loaded by default, so you won't normally need to do this
log4js.addAppender(log4js.appenders.file('logs/cheese.log'), 'cheese');

var logger = log4js.getLogger('cheese');

logger.trace('Entering cheese testing');
logger.debug('Got cheese.');
logger.info('Cheese is Gouda.');
logger.warn('Cheese is quite smelly.');
logger.error('Cheese is too ripe!');
logger.fatal('Cheese was breeding ground for listeria.');


[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.

The first 5 lines of the code above could also be written as:

var log4js = require('log4js');
  appenders: [
    { type: 'console' },
    { type: 'file', filename: 'logs/cheese.log', category: 'cheese' }


You can configure the appenders and log levels manually (as above), or provide a configuration file (log4js.configure('path/to/file.json')), or a configuration object. The configuration file location may also be specified via the environment variable LOG4JS_CONFIG (export LOG4JS_CONFIG=path/to/file.json). An example file can be found in test/vows/log4js.json. An example config file with log rolling is in test/vows/with-log-rolling.json. You can configure log4js to check for configuration file changes at regular intervals, and if changed, reload. This allows changes to logging levels to occur without restarting the application.

To turn it on and specify a period:

log4js.configure('file.json', { reloadSecs: 300 });

For FileAppender you can also pass the path to the log directory as an option where all your log files would be stored.

log4js.configure('my_log4js_configuration.json', { cwd: '/absolute/path/to/log/dir' });

If you have already defined an absolute path for one of the FileAppenders in the configuration file, you could add a "absolute": true to the particular FileAppender to override the cwd option passed. Here is an example configuration file:


  "appenders": [
      "type": "file",
      "filename": "relative/path/to/log_file.log",
      "maxLogSize": 20480,
      "backups": 3,
      "category": "relative-logger"
      "type": "file",
      "absolute": true,
      "filename": "/absolute/path/to/log_file.log",
      "maxLogSize": 20480,
      "backups": 10,
      "category": "absolute-logger"          

Documentation for most of the core appenders can be found on the wiki, otherwise take a look at the tests and the examples.


See the wiki. Improve the wiki, please.

There's also an example application.


Contributions welcome, but take a look at the rules first.


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.