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3.18.0 • Public • Published

LSK.js – log

@lskjs/log – Логгер совмещающий лучшие черты morgan, winston, bunyan, logrus. debug. Базируется на debug-level.

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⌨️ Install

# yarn
yarn i @lskjs/log 

# npm
npm i @lskjs/log 


$ npm install --save @lskjs/log


@lskjs/log provides 6 log levels which are trace, debug, info, warn, error, fatal, and off.

Each level has a corresponding method debug -> log.debug ... fatal --> log.fatal which shall be used to indicated the level to log.

The characters %s, %d, %i, %f, %j, %o, %O, %% are supported formatters when given in the first argument.


const Log = require('@lskjs/log')
// creates a logger for <namespace> `test`
const log = new Log('test')

// or using a global Log instance
const log = require('@lskjs/log').log('test')

log.fatal(new Error('fatal'))        // logs an Error at level FATAL
log.error(new Error('boom'))         // logs an Error at level ERROR
log.warn('huh %o', {ghost: 'rider'}) // logs a formatted object at level WARN
log.info('%s world', 'hello')        // logs a formatted string at level INFO
log.debug({object: 1})               // logs an object at level DEBUG
log.log('always logs')               // always logs regardless of set level

Running levels.js without environment variables will show no output (apart from log.log). Setting only DEBUG_LEVEL shows all lines with their respective level. Combined with DEBUG, using comma separated namespaces, only those log lines with matching namespace and level get logged.

The following table gives an overview of possible combinations:

-- -- no output
fatal -- logs only log.fatal
error -- log.fatal, log.error
warn -- log.fatal, log.error, log.warn
info -- log.fatal, log.error, log.warn and log.info
debug -- log.fatal, log.error, log.warn, log.info and log.debug
trace -- log.fatal, log.error, log.warn, log.info, log.debug and log.trace
-- <namespaces> log.fatal, to log.debug which apply to <namespaces>.
Same behavior as debug.
fatal <namespaces> log.fatal for all <namespaces> only
error <namespaces> log.fatal, log.error for <namespaces> only
warn <namespaces> log.fatal, to log.warn for <namespaces> only
info <namespaces> log.fatal, to log.info for <namespaces> only
debug <namespaces> log.fatal, to log.debug for <namespaces> only
trace <namespaces> log.fatal, to log.trace for <namespaces> only
-- error:n1,debug:n2,fatal:* Logs namespace n1 at level error, namespace n2 at level debug and all other namespaces (*) at level fatal
datal error:n1,n2 Logs n1 at level error, n2 at level fatal. All other namespaces will NOT get logged


Run the server.js example with different settings:

No output

$ node examples/server.js

Logging .info and .error

$ DEBUG_LEVEL=info node examples/server.js

Logging .error for server only

$ DEBUG_LEVEL=error DEBUG=server node examples/server.js

Logging .error in production mode (JSON without colors)

$ NODE_ENV=production DEBUG_LEVEL=error node examples/server.js

Behavior is as with debug.

$ DEBUG=server,client:A node examples/server.js

Log server at level info, and all other modules at level error

$ DEBUG=info:server,error:* node examples/server.js


Environment Variables


Setting | Values | Description ---- | ---- | ---- DEBUG | | Enables/disables specific debugging namespaces DEBUG_LEVEL | error, warn, info, debug | sets debug level DEBUG_COLORS | true/false | display colors (if supported)

Node only

Setting | Values | NODE_ENV=
development | Description ---- | ---- | ---- | ---- DEBUG_JSON | true/false | false | use JSON format instead of string based log DEBUG_SERVERINFO | true/false | false | adds server information like pid and hostname DEBUG_HIDE_DATE | true/false | false | hides date from log output default false

For NODE_ENV !== 'development' the default logging is in JSON format using serverinfo and date.

Browsers only

Setting | Values | Description ---- | ---- | ---- DEBUG_URL | URL | log in JSON format to server (needs middleware.js at the server side)

In the browser localStorage is used to set/save the settings. E.g. to enable level ERROR an all namespaces type in console and refresh your page/ app:



You may set the global log options with:


const fs = require('fs')
const Log = require('@lskjs/log')

// log into file instead of process.stderr
const stream = fs.createWriteStream('./my.log')

// The options will be set for all Loggers...
  level: 'DEBUG',
  json: true,
  serverinfo: true,
  hideDate: false,
  colors: false,
const log = new Log('*')

log.debug({object: 1}) // ...

Option name | Setting | env | Type | Description ----- | ---- | ---- | ---- | ---- level | DEBUG_LEVEL | both | String | namespaces | DEBUG | both | String | json | DEBUG_JSON | node | Boolean | spaces | DEBUG_SPACES | node | Number | JSON spaces hideDate | DEBUG_HIDE_DATE | both | Boolean | colors | DEBUG_COLORS | both | Boolean | stream | -- | node | Stream | output stream (defaults to process.stderr) url | DEBUG_URL | browser | String | formatters | -- | both | Object | custom formatters


(From bunyan)

  • fatal: The service/app is going to stop or becomes unusable. An operator should definitely look into this soon.
  • error: Fatal for a particular request, but the service/app continues servicing. An operator should look at this soon(ish)
  • warn: A note on something that should probably be looked at by an operator eventually.
  • info: Detail on regular operation.
  • debug: Anything else, i.e. too verbose to be included in INFO level.
  • trace: Anything else, i.e. too verbose to be included in INFO level.


Namespaces select dedicated packages for logging (check Conventions) considering the level selected with DEBUG_LEVEL. To choose a different log-level prefix the namespace with the level to be set for that namespace.

E.g. to log all packages on level FATAL, test on ERROR, log:A on WARN. As a side-effect * will also cause all modules using debug being logged.

$ DEBUG_LEVEL=fatal DEBUG=ERROR:test,WARN:log:A,* node examples/levels.js
  ERROR test Error: boom
  FATAL test fatal test +7ms
  WARN log:A huh {"ghost":"rider"} +0ms
  ERROR log:A Error: baam
  FATAL log:A fatal A +1ms
  FATAL log:B fatal B +0ms
  using-debug using debug +0ms
  using-debug:A using debug - feature A +1ms

So maybe consider using DEBUG=...,FATAL:* instead:

$ DEBUG=error:test,warn:log:A,fatal:*,using-debug:* node examples/levels.js
  ERROR test Error: boom
  FATAL test fatal test +7ms
  WARN log:A huh {"ghost":"rider"} +0ms
  ERROR log:A Error: baam
  FATAL log:A fatal A +1ms
  FATAL log:B fatal B +0ms
  using-debug:A using debug - feature A +1ms


(from debug)

If you're using this in one or more of your libraries, you should use the name of your library so that developers may toggle debugging as desired without guessing names. If you have more than one debuggers you should prefix them with your package name and use ":" to separate features. For example bodyParser from Connect would then be connect:bodyParser. If you append a * to the end of your name, it will always be enabled regardless of the setting of the DEBUG environment variable. You can then use it for normal output as well as debug output.


(from debug)

The * character may be used as a wildcard. Suppose for example your library has debuggers named connect:bodyParser, connect:compress, connect:session, instead of listing all three with DEBUG=connect:bodyParser,connect:compress,connect:session, you may simply do DEBUG=connect:*, or to run everything using this module simply use DEBUG=*.

You can also exclude specific debuggers by prefixing them with a - character. For example, DEBUG=*,-connect:* would include all debuggers except those starting with connect:.


@lskjs/log supports two types of outputs

  1. human readable - this pretty much follows the output of debug This is the default for NODE_ENV=development. Can be forced using DEBUG_JSON=0
  2. machine readable - JSON output (similar to bunyan) This is the default for test/production envs. Can be forced using DEBUG_JSON=1

JSON output

When using %j, %o, %O all will expand to %j JSON, so there is no difference when using in node.

Nonetheless it is not recommended to use these formatters for logging errors and objects as this complicates later log inspection.

Each log records into a single JSON stringified line.

Core fields are:

  • level: One of the five log levels.
  • name: The name of the namespace logged.
  • msg: A message which should give reason for logging the line.
  • hostname: Hostname of the server. (Requires option serverinfo)
  • pid: PID of the logged process. (Requires option serverinfo).
  • time: Timestamp (Suppress with option hideDate).
  • diff: Difftime in milliseconds.

See examples/jsonOutput.js.

When logging a message string, number or a formatted string it will show up under msg like:

log.debug('a %s, a number %d, an %o and %j', 'string', 1.2, {object: 1}, {NOT: 'RECOMMENDED'})
// >
{ "level": "DEBUG",           // log level
  "name": "package:feature",  // the namespace of the logger
  "msg": "a string, a number 1.2, an {\"object\":1} and {\"NOT\":\"RECOMMENDED\"}", // the formatted message
  "hostname": "server",       // server hostname
  "pid": 8310,                // process pid
  "time": "2017-11-08T21:01:00.025Z", // timestamp as ISOString
  "diff": 5                   // difftime in ms

Objects without formatters get assigned, arrays will show up under arr:

log.info({object: 1}, {json: true}, [1, 2, 3], '%s #%d', 'message', 1)
// >
{ "level": "INFO",
  "name": "package:feature",
	"msg": "message #1"
  "object": 1,
	"json": true,
  "arr": [1,2,3],
  "time": "2017-11-09T21:09:49.482Z",
  "diff": 0

An error gets logged under err

const err = new TypeError('bam')
err.status = 500
log.error(err, {object: 1}) // you may add an additional object
// >
{ "level":"ERROR",
  "err": { // the error object
    "stack":"Error: bam\n    at Object.<anonymous> (...\n    at bootstrap_node.js:608:3",
    "status": 500
  "object": 1,

Custom formatters

You may use custom formatters e.g. to display numbers converted into hex-format.


const Log = require('..')
Log.options({level: 'debug'})
const log = new Log('test', {formatters: {
  h: (n) => `x${n.toString(16).toUpperCase()}`

log.debug('%h', 255) // logs 255 as hex 'xFF'


If logging an object you may define a toJSON() function on that object to change proper logging of the object itself:


const Log = require('@lskjs/log')
const log = new Log('*')

function reqToJSON () {
  const {ip, method, url} = this
  return {ip, method, url}

// assume a request obj
const req = {
  method: 'GET', url: '/path', ip: '',
  headers: {'user-agent': 'Custom/2.0'}, connection: {/* ... */}
req.toJSON = reqToJSON.bind(req)

log.debug({req: req})
//> DEBUG * {"req":{"ip":"","method":"GET","url":"/path"}} +0ms

Logging Browser messages

To log debug messages from the browser on your server you can enable a logger middleware in your express/ connect server.

const app = require('express')()
const {logger} = require('@lskjs/log')

app.use('./@lskjs/log', logger({maxSize: 100}))

In your single page application use:

import Log from '@lskjs/log'

localStorage.setItem('DEBUG_URL', '/api/log')
localStorage.setItem('DEBUG', 'myApp*')
// ...
const log = new Log('myApp')

log.debug('my first %s', 'logline')

Check example at examples/app. To run it use:

DEBUG=* node examples/app/server.js

and open http://localhost:3000


Inspired by

📖 License

This project is licensed under the MIT License - see the LICENSE file for details

👥 Contributors

Igor Suvorov

💻 🎨 🤔

👏 Contributing

  1. Fork it (https://github.com/yourname/yourproject/fork)
  2. Create your feature branch (git checkout -b features/fooBar)
  3. Commit your changes (git commit -am 'feat(image): Add some fooBar')
  4. Push to the branch (git push origin feature/fooBar)
  5. Create a new Pull Request

📮 Any questions? Always welcome :)

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