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 log rolling based on file size
- SMTP appender
- GELF appender
- hook.io appender
- Loggly appender
- Logstash UDP 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
var log4js = ;var logger = log4js;logger;
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 = ;//console log is loaded by default, so you won't normally need to do this//log4js.loadAppender('console');log4js;//log4js.addAppender(log4js.appenders.console());log4js;var logger = log4js;logger;logger;logger;logger;logger;logger;logger;
[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
The first 5 lines of the code above could also be written as:
var log4js = ;log4js;
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
An example file can be found in
test/log4js.json. An example config file with log rolling is in
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:
For FileAppender you can also pass the path to the log directory as an option where all your log files would be stored.
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:
Documentation for most of the core appenders can be found on the wiki, otherwise take a look at the tests and the examples.
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.