anylogger

anylogger _^1.0.11

Get a logger. Any logger.

The logger for libraries

When we want to do logging from a library, we don't want to force the choice of logging framework on the application developer. Instead, we want to use whatever logging framework the application developer selected. anylogger let's you do just that.

Quickstart

Library	App with debug	App with loglevel	App with ulog	App with log4js
Install npm i -P anylogger Use import anylogger from 'anylogger' const log = anylogger('my-library') log('Anylogger is easy!') Install your preferred logger and it's adapter as dev dependencies.	Install npm i -P anylogger debug anylogger-debug Add to entry point index.js import "anylogger-debug" Use import anylogger from 'anylogger' const log = anylogger('my-app') log('Anylogger is easy!')	Install npm i -P anylogger loglevel anylogger-loglevel Add to entry point index.js import "anylogger-loglevel" Use import anylogger from 'anylogger' const log = anylogger('my-app') log('Anylogger is easy!')	Install npm i -P anylogger ulog Add to entry point index.js import "ulog" Use import anylogger from 'anylogger' const log = anylogger('my-app') log('Anylogger is easy!')	Install npm i -P anylogger log4js anylogger-log4js Add to entry point index.js import "anylogger-log4js" Use import anylogger from 'anylogger' const log = anylogger('my-app') log('Anylogger is easy!')

What is this?

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 challenge. 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 ~330 bytes logging facade that you can include in your library to support logging, 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 ~330 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?

Download

• anylogger.js (fully commented source ~5kB)
• anylogger.min.js (minified 532 bytes, gzipped ~330 bytes)

CDN

index.html

<script src="https://unpkg.com/anylogger@1.0.11"></script>
<script>(function(){ // IIFE
  var log = anylogger('index.html')
  log.info('Logging is simple!')
})()</script>

Note that anylogger by default does nothing. You need an adapter to see output. For example, to send all logging to the console, you can use anylogger-console.

Install

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

Install in a library project

If you are building a library, install anylogger as a dependency:

npm install --save anylogger

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

Install dev dependencies in a library project

If you are building a library, you can use the logging framework you prefer without tightly coupling your library to it by installing that library and the adapter for it if needed as development dependencies:

For anylogger-console:

npm install --save-dev anylogger-console

For debug:

npm install --save-dev debug anylogger-debug

See anylogger-debug

For loglevel:

npm install --save-dev loglevel anylogger-loglevel

See anylogger-loglevel

For ulog:

npm install --save-dev ulog

No adapter is needed for ulog

For log4js:

npm install --save-dev log4js anylogger-log4js

See anylogger-log4js

Install in an application project

If you are building an application project and have selected a logging framework, install anylogger, the selected logging framework and the adapter for that logging framework if needed.

For anylogger-console:

npm install --save anylogger anylogger-console

For debug:

npm install --save anylogger debug anylogger-debug

See anylogger-debug

For loglevel:

npm install --save anylogger loglevel anylogger-loglevel

See anylogger-loglevel

For ulog

npm install --save anylogger ulog

No adapter is needed for ulog

For log4js:

npm install --save anylogger log4js anylogger-log4js

See anylogger-log4js

Check out all available adapters.

Include

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

Include in a library

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

require

my-library.js

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

import

my-library.js

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

This way, your library does not get tightly coupled to any specific logger

Include in tests for your library

In the tests for your library code, you can include an adapter and make your library use the logging framework of your choice without having to add it as a dependency for your library. You can add them as development dependencies.

require

my-library.test.js

// e.g. for ulog
require('ulog')
// all anylogger loggers will use ulog
var log = require('anylogger')('my-lbrary:test')

import

my-library.test.js

// e.g. for ulog
import 'ulog'
// all anylogger loggers will use ulog
import anylogger from 'anylogger'
const log = anylogger('my-lbrary:test')

Include in an application project

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

require

main.js

// e.g. for debug
require('anylogger-debug')
// all anylogger loggers will use debug

import

main.js

// e.g. for debug
import 'anylogger-debug'
// all anylogger loggers will use debug

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

require

my-module.js

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

import

my-module.js

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 log message')
log('debug', 'A debug message')
log('warn', 'A warning message')
log.info(log.name + ' starting...')
log.error('Something went wrong', new Error('Oh no!'))
if (log.enabledFor('warn')) {
  log.warn(expensiveArguments())
}

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.

log.info('Logging is easy!')

Anylogger API

So what does this API look like?

anylogger

function anylogger(name, options) => logger

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

name

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.

options

An optional options object. Object. Optional. Defaults to undefined. The use of such options 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 options object it is given on to anylogger.new 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 anylogger.new.

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:

log.debug('message')
log.info('message')

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)
log.info: function(...args)
log.log: function(...args)
log.debug: function(...args)
log.trace: function(...args)
log.enabledFor: function(level) => truthy or falsey

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

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.

anylogger.new

anylogger.new(name, options) => logger

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

Uses new Function(..) to create a named function so that function.name corresponds to the module name given. Polyfills function.name on platforms where it is not natively available.

name

The name of the new logger. String. Required.

options

An optional options object. Object. Optional.

If the logging framework you are writing an adapter for uses an options object, you should override anylogger.new and do something useful with the options object here (set it as a property on the logger for example), because the default implementation just ignores it.

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 = anylogger.new

// override anylogger.new
anylogger.new = (name, options) => {
  // call the original function to chain it
  var logger = make(name, options)
  // do something useful with the options object
  logger.options = options
  // return the customized logger
  return logger
}

All anylogger methods are independent of this so they can all be easily chained

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

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

logger

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

The default implementation loops over the anylogger.levels and creates noop methods for each level. Additionally it creates a noop enabledFor that always returns undefined.

You can override or chain this method to change the way the log methods are (re-)created. In a library that supports log levels, all methods corresponding to log levels equal to or higher than the currently active level might be replaced with console 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

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

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

• Jakub Jirutka who contributed TypeScript type declarations.
• TJ Holowaychuk for writing debug
• Tim Perry for writing loglevel
• The authors of log4js, log4js-node, morgan, bunyan, pino and all other log libraries out there

Issues

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

Copyright

© 2020 by Stijn de Witt. Some rights reserved. Contributions by Jakub Jirutka.

License

Licensed under the MIT Open Source license.

gzip-size

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.