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
• replacement of node's console.log functions (optional)
• file appender, with log rolling based on file size
• SMTP appender
• GELF appender
• hook.io 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.)

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.loadAppender('console');
log4js.loadAppender('file');
//log4js.addAppender(log4js.appenders.console());
log4js.addAppender(log4js.appenders.file('logs/cheese.log'), 'cheese');

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

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.');

Output:

[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');
log4js.configure({
  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/log4js.json. An example config file with log rolling is in test/with-log-rolling.json. By default, the configuration file is checked for changes every 60 seconds, and if changed, reloaded. This allows changes to logging levels to occur without restarting the application.

To turn off configuration file change checking, configure with:

var log4js = require('log4js');
log4js.configure('my_log4js_configuration.json', {});

To specify a different 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:

#### my_log4js_configuration.json ####
{
  "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.

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.