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0.18.0 • Public • Published

anylogger 0.18.0

Get a logger. Any logger.

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A logger for libraries

Get whatever logging framework the host project is using, or a wrapper around the console, or a dummy log object that does nothing. Anything really, that will let your library do logging without you having to decide what logging framework the app using your library should use.

Anylogger will let the user of your library pick the logger for his app, and will let your library pick up on whatever choice he made and run with it.

By choosing anylogger, you are explicitly not choosing any specific logging framework, but instead are limiting yourself to the Anylogger API, a small API that only captures the bare essentials for logging, but because of that, is compatible with nearly every logging library out there.

A logging facade

We, the Javascript community, really need a logging facade. There are dozens of logging libraries around and we library authors face a dilemma. Which logger do we pick? Should we make this configurable? Should we just not log? Use the console directly? How do we deal with this complexity?

In software architecture, a facade hides a complex system behind a simple interface. In the context of our logging problem, we can have our library log to a simple facade object. In our application we back the facade object by the actual logging framework with an adapter.

So what we need is a simple and small logging facade and a bunch of adapters for popular loggers.

Introducing anylogger

A tiny ~350 bytes logging facade that you can include in your library to have logging 'just work', while at the same time allowing application developers to plug in any logging framework they choose.

Instead of building in your own library specific configuration mechanism, or forcing the choice for a certain logging framework on your users, or just abandoning logging altogether, choose anylogger and for just ~350 bytes shared between all libraries doing this, we can plug in any framework of our choice and all libraries will automatically start to use that framework. Wouldn't it be much better and easier?

At the application level, the app developers choose whatever logging framework they prefer and install the anylogger-to-their-framework adapter. They make sure to require the adapter in the application entry point and from that point on, any library using anylogger will automatically start using the selected logging framework.




<script src=""></script>
<script>(function(){ // IIFE
  var log = anylogger('index.html')'Logging is simple!')


Depending on your project type, install just anylogger, or anylogger + your logging framework of choice + an anylogger adapter if needed.

Install in a library project

If you are building a library, just install anylogger:

npm install --save anylogger

This will add anylogger as a dependency to your package.json.

To enforce that your library ends up using the same anylogger version as the application itself, add anylogger as a peer dependency:

  "peerDependencies": {
    "anylogger": "^0.18.0"

You can just copy the entry from dependencies, it should be the same.

When the user installs our library, if the peer dependency is not satisfied by the project, NPM will warn about it during installation.

Install in an application project

If you are building an application project and have selected a logging framework, in addition to installing anylogger itself, install the selected logging framework and the anylogger adapter for that logging framework.

For example for debug:

npm install --save anylogger debug anylogger-debug

This installs anylogger-debug.

or, for ulog which has native anylogger support since v2:

npm install --save anylogger ulog

Because ulog supports anylogger natively, we don't need an adapter

Check out all available adapters.


Depending on your project type, either just use anylogger, or also include the adapter.

Include in a library

In your libraries, only use anylogger and restrict yourself to the Anylogger API to stay framework-independent:



var log = require('anylogger')('my-library')



import anylogger from 'anylogger'
const log = anylogger('my-library')

Include in an application project

In your main entry point, include your adapter or library with native support so it extends anylogger:



// for debug
var debug = require('debug')
// libraries now use debug
// or, for ulog
var ulog = require('ulog') 
// native support! no adapter needed :)
// libraries now use ulog
// etc, see the specific library or adapter for details on anylogger support



// for debug
import debug from 'debug' 
import 'anylogger-debug'
// libraries now use debug
debug.enable('my-library') // enable debug mode
// or, for ulog
import ulog from 'ulog' 
// native support! no adapter needed :)
// libraries now use ulog
ulog.enable('my-library') // enable debug mode

In your other modules, use only anylogger and restrict yourself to the Anylogger API to stay framework-independent:



var log = require('anylogger')('my-module')



import anylogger from 'anylogger'
const log = anylogger('my-module')

Using anylogger

Anylogger is very natural to use:

var log = require('anylogger')('my-module')
log('A debug message')
log('warn', 'A warning message') + ' starting...')
log.error('Something went wrong', new Error('Oh no!'))

If you are able to restrict yourself to the Anylogger API, your code will be framework independent and will work with any supported logging library.'Logging is easy!')
// Avoid using methods like log.silly() and log.time() etc which are only 
// supported in some frameworks and not in others and your code will work 
// with any supported logging framework without any changes

Anylogger API

So what does this API look like?


function anylogger(name, config) => logger

The main function to call to get a logger. Accepts two arguments.


The name of the logger. String. Optional. Defaults to undefined. The recommended format is <package-name>[:<sub>[:<sub> [..]]], as this is the convention used by the highly popular debug module. But you are free to pick any name you want. You only get a logger if you supply a name. If the name is not given anylogger() will return an object containing all loggers, keyed by name.


An optional config object. Object. Optional. Defaults to undefined. The use of such config objects varies wildly amongst implementations so it is recommended to avoid using it where possible. However in case of implementations that require it, anylogger passes any config object it is given on to to allow it to be used where needed.

When no arguments are given anylogger returns an object containing all loggers created so far, keyed by name.

When a name is given anylogger returns the existing logger with that name, or creates a new one by calling

The returned logger adheres to the Logging API described below.

Logging API

The logger returned by anylogger is a function that can do logging on it's own:

log('message')          // logs a message at `log` level
log('info', 'message')  // logs a message at `info` level

In addition, the logger looks like a simple console object:


Because of this, the logger created by anylogger is compatible with most logging frameworks out there, which mostly use one or both of these approaches.

The main API looks like this (in pseudo code):

log: function(level='log', ...args)
log.error: function(...args)
log.warn: function(...args) function(...args)
log.log: function(...args)
log.debug: function(...args)
log.trace: function(...args)

And that's about it. However this covers the basic logging needs.

Note that all logging methods here are part of the upcoming Console standard, but not all platforms and frameworks support all of them. In particular the debug method is not available everywhere. Anylogger will make sure that the debug function is polyfilled if needed.

Is your logging framework not supported? No fear, just...

Write an anylogger adapter

To write an anylogger adapter, you need to make a project that includes both anylogger and the logging framework the adapter is for as peer dependencies.

You then need to modify one or more of the anylogger extension points so the created loggers will be compliant with both the anylogger Logging API as well as with the logging framework's own API.

It is recommended you call your library anylogger-[adapter], where [adapter] should be replaced with the name of the logging framework the adapter is for. For example, the adapter for debug is called anylogger-debug.

In addition, it is recommended you add the keyword "anylogger" to the package.json file of your adapter project, so it will show up in the list of available adapters.

anylogger extension points

The process of logger creation and invocation is split up in such a way as to optimize possible extension points allowing extensions to re-use anylogger functionality and avoid having to duplicate code. The extension points are:


anylogger.levels = {error:1, warn:2, info:3, log:4, debug:5, trace:6}

An object containing a mapping of level names to level values.

To be compliant with the anylogger API, loggers should support at least the log methods corresponding to the default levels, but they may define additional levels and they may choose to use different numeric values for all the levels.

The guarantees the Anylogger API makes are:

  • there is a logging method corresponding to each level listed in anylogger.levels
  • the levels error, warn, info, log, debug and trace are always there
  • each level corresponds to a numeric value

Note that the Anylogger API explicitly does not guarantee that all levels have distinct values or that the numeric values will follow any pattern or have any specific order. For this reason it is best to think of levels as separate log channels, possibly going to different output locations.

You can replace or change this object to include levels corresponding with those available in the framework you are writing an adapter for. Please make sure to always include the default levels as well so all code can rely on the 6 console methods error, warn, info, log, debug and trace to always be there., config) => logger

Creates a new logger function that calls anylogger.log when invoked.

Uses some evil eval trickery to create a named function so that corresponds to the module name given. Polyfills on platforms where it is not natively available.


The name of the new logger. String. Required.


An optional config object. Object. Optional.

Instead of completely trying to replace the original method, I recommend you chain it to include your one-time customizations like this:

import anylogger from 'anylogger'
// save the original function
const make =
// override = (name, config) => {
  // call the original function to chain it
  var logger = make(name, config)
  // add your customizations
  logger.myCoolFeature = function(){'My cool feature!')}
  // return the customized logger
  return logger

If you need to re-apply customizations any time relevant config changes (such as active log level changing), override anylogger.ext.


anylogger.ext(logger) => logger

Called when a logger needs to be extended, either because it was newly created, or because it's configuration or settings changed in some way.

This method must ensure that a log method is available on the logger for each level in anylogger.levels.

When overriding anylogger.ext, please ensure the function can safely be called multiple times on the same object


The logger that should be (re-)extended. Function. Required.

The default implementation loops over the anylogger.levels and creates log methods for each level. You can override or chain this method to change the way the log methods are (re-)created. By default, all log methods will delegate to the native console. But in a library that supports log levels, all methods corresponding to log levels lower than the currently active levels might be replaced with no-op methods instead. Or maybe the destination of the log messages might change dynamically based on configuration. Apply such changes in anylogger.ext as it will be called again whenever relevant config changes. This allows adapters to (re-)extend the logger so that the new configuration takes effect.

You may need to ensure in your adapter that anylogger.ext is called whenever relevant config changes. By hooking into setters for example.


anylogger.log([level='log'], ...args)

The log function returned by anylogger calls anylogger.log, which determines the log level and invokes the appropriate log method.

Please have a look at the source it should make it more clear how to write an adapter. Also consider studying the available adapters and learn by example.

Give something back

If you wrote an anylogger adapter, make sure to share it back with the community. Publish it to NPM for all to use!


Credits go to these people, who helped with this project:


Add an issue in this project's issue tracker to let me know of any problems you find, or questions you may have.


© 2019 by Stijn de Witt. Some rights reserved. Contributions by Jakub Jirutka.


Licensed under the MIT Open Source license.


The GZIP algorithm is available in different flavours and with different possible compression settings. The sizes quoted in this README have been measured using gzip-size by Sindre Sorhus, your mileage may vary.


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