Logging for node.js
Switch branches/tags
Nothing to show
Clone or download
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Failed to load latest commit information.



This is a considerable departure from the traditional logger.

This logger is meant for use in third party modules and packages. It's so that modules can have a very simple way to offer optional visibility in to the modules inner workings.

To this end, it does not have log levels like info, warn, etc. It simply allows the creation of a logger for your module (with a name) and offer a single function to take messages and a context for those messages.

This module is both an implementation and a light specification. Loggers can be quite opinionated and the creators of modules are unlikely to solidify around a single implementation of anything.


A logging library should be a single function that returns logger functions.

var logging = require('logging')
  , log = logging('mymodulename')

When running an application in a production environment, logging is the one of the few things you need to be global that is outside of node core.

Users of this specification should require the user to set the process.logging to the desired module. A library must never set this property automatically as it will override any other logger the user may want to use.


process.logging = require('logging')
var request = require('request')

Notice that this line comes before loading any other module. This is important, modules will likely check for process.logging as soon as they are required.

Using the logger is quite easy within a module.

if (process.logging) var log = process.logging('mymodule')
else var log = function () {}

module.exports = fancy (options) {
  log('new fancy %method for %url', options)
fancy({method:'GET', url:'http://www.google.com'})

The final piece of this spec is visible in the last example.

Log functions take two arguments, a message and a context.

Named string interpolation from the context should be supported. This prevents many errors related to using the + operator in building the message string.

logging API

The rest of this documentation covers features which should not be considered part of the specification.

Enabling stdout or stderr printing of logs.


All will print [mymodule] new fancy GET for http://www.google.com.