A logger for just about everything.
See the Upgrade Guide for more information. Bug reports and PRs welcome!
Looking for [email protected]
documentation?
Please note that the documentation below is for winston@3
.
Read the [email protected]
documentation.
winston
is designed to be a simple and universal logging library with
support for multiple transports. A transport is essentially a storage device
for your logs. Each winston
logger can have multiple transports (see:
Transports) configured at different levels (see: Logging levels). For
example, one may want error logs to be stored in a persistent remote location
(like a database), but all logs output to the console or a local file.
winston
aims to decouple parts of the logging process to make it more
flexible and extensible. Attention is given to supporting flexibility in log
formatting (see: Formats) & levels (see: Using custom logging levels), and
ensuring those APIs decoupled from the implementation of transport logging
(i.e. how the logs are stored / indexed, see: Adding Custom Transports) to
the API that they exposed to the programmer.
TL;DR? Check out the quick start example in ./examples/
.
There are a number of other examples in ./examples/*.js
.
Don't see an example you think should be there? Submit a pull request
to add it!
The recommended way to use winston
is to create your own logger. The
simplest way to do this is using winston.createLogger
:
const winston = require('winston');
const logger = winston.createLogger({
level: 'info',
format: winston.format.json(),
defaultMeta: { service: 'user-service' },
transports: [
//
// - Write all logs with importance level of `error` or less to `error.log`
// - Write all logs with importance level of `info` or less to `combined.log`
//
new winston.transports.File({ filename: 'error.log', level: 'error' }),
new winston.transports.File({ filename: 'combined.log' }),
],
});
//
// If we're not in production then log to the `console` with the format:
// `${info.level}: ${info.message} JSON.stringify({ ...rest }) `
//
if (process.env.NODE_ENV !== 'production') {
logger.add(new winston.transports.Console({
format: winston.format.simple(),
}));
}
You may also log directly via the default logger exposed by
require('winston')
, but this merely intended to be a convenient shared
logger to use throughout your application if you so choose.
Note that the default logger doesn't have any transports by default.
You need add transports by yourself, and leaving the default logger without any
transports may produce a high memory usage issue.
- Motivation
- Quick Start
- Usage
- Table of Contents
- Logging
- Formats
- Logging levels
- Transports
- Exceptions
- Rejections
- Profiling
- Streaming Logs
- Querying Logs
- Further Reading
- Installation
- Run Tests
Logging levels in winston
conform to the severity ordering specified by
RFC5424: severity of all levels is assumed to be numerically ascending
from most important to least important.
const levels = {
error: 0,
warn: 1,
info: 2,
http: 3,
verbose: 4,
debug: 5,
silly: 6
};
You get started by creating a logger using winston.createLogger
:
const logger = winston.createLogger({
transports: [
new winston.transports.Console(),
new winston.transports.File({ filename: 'combined.log' })
]
});
A logger accepts the following parameters:
Name | Default | Description |
---|---|---|
level |
'info' |
Log only if info.level is less than or equal to this level |
levels |
winston.config.npm.levels |
Levels (and colors) representing log priorities |
format |
winston.format.json |
Formatting for info messages (see: Formats) |
transports |
[] (No transports) |
Set of logging targets for info messages |
exitOnError |
true |
If false, handled exceptions will not cause process.exit |
silent |
false |
If true, all logs are suppressed |
The levels provided to createLogger
will be defined as convenience methods
on the logger
returned.
//
// Logging
//
logger.log({
level: 'info',
message: 'Hello distributed log files!'
});
logger.info('Hello again distributed logs');
You can add or remove transports from the logger
once it has been provided
to you from winston.createLogger
:
const files = new winston.transports.File({ filename: 'combined.log' });
const console = new winston.transports.Console();
logger
.clear() // Remove all transports
.add(console) // Add console transport
.add(files) // Add file transport
.remove(console); // Remove console transport
You can also wholesale reconfigure a winston.Logger
instance using the
configure
method:
const logger = winston.createLogger({
level: 'info',
transports: [
new winston.transports.Console(),
new winston.transports.File({ filename: 'combined.log' })
]
});
//
// Replaces the previous transports with those in the
// new configuration wholesale.
//
const DailyRotateFile = require('winston-daily-rotate-file');
logger.configure({
level: 'verbose',
transports: [
new DailyRotateFile(opts)
]
});
You can create child loggers from existing loggers to pass metadata overrides:
const logger = winston.createLogger({
transports: [
new winston.transports.Console(),
]
});
const childLogger = logger.child({ requestId: '451' });
In winston
, both Logger
and Transport
instances are treated as
objectMode
streams that accept an info
object.
The info
parameter provided to a given format represents a single log
message. The object itself is mutable. Every info
must have at least the
level
and message
properties:
const info = {
level: 'info', // Level of the logging message
message: 'Hey! Log something?' // Descriptive message being logged.
};
Properties besides level and message are considered as "meta
". i.e.:
const { level, message, ...meta } = info;
Several of the formats in logform
itself add additional properties:
Property | Format added by | Description |
---|---|---|
splat |
splat() |
String interpolation splat for %d %s -style messages. |
timestamp |
timestamp() |
timestamp the message was received. |
label |
label() |
Custom label associated with each message. |
ms |
ms() |
Number of milliseconds since the previous log message. |
As a consumer you may add whatever properties you wish – internal state is
maintained by Symbol
properties:
Symbol.for('level')
(READ-ONLY): equal tolevel
property. Is treated as immutable by all code.Symbol.for('message'):
complete string message set by "finalizing formats":json
logstash
printf
prettyPrint
simple
Symbol.for('splat')
: additional string interpolation arguments. Used exclusively bysplat()
format.
These Symbols are stored in another package: triple-beam
so that all
consumers of logform
can have the same Symbol reference. i.e.:
const { LEVEL, MESSAGE, SPLAT } = require('triple-beam');
console.log(LEVEL === Symbol.for('level'));
// true
console.log(MESSAGE === Symbol.for('message'));
// true
console.log(SPLAT === Symbol.for('splat'));
// true
NOTE: any
{ message }
property in ameta
object provided will automatically be concatenated to anymsg
already provided: For example the below will concatenate 'world' onto 'hello':logger.log('error', 'hello', { message: 'world' }); logger.info('hello', { message: 'world' });
Formats in winston
can be accessed from winston.format
. They are
implemented in logform
, a separate
module from winston
. This allows flexibility when writing your own transports
in case you wish to include a default format with your transport.
In modern versions of node
template strings are very performant and are the
recommended way for doing most end-user formatting. If you want to bespoke
format your logs, winston.format.printf
is for you:
const { createLogger, format, transports } = require('winston');
const { combine, timestamp, label, printf } = format;
const myFormat = printf(({ level, message, label, timestamp }) => {
return `${timestamp} [${label}] ${level}: ${message}`;
});
const logger = createLogger({
format: combine(
label({ label: 'right meow!' }),
timestamp(),
myFormat
),
transports: [new transports.Console()]
});
To see what built-in formats are available and learn more about creating your
own custom logging formats, see logform
.
Any number of formats may be combined into a single format using
format.combine
. Since format.combine
takes no opts
, as a convenience it
returns pre-created instance of the combined format.
const { createLogger, format, transports } = require('winston');
const { combine, timestamp, label, prettyPrint } = format;
const logger = createLogger({
format: combine(
label({ label: 'right meow!' }),
timestamp(),
prettyPrint()
),
transports: [new transports.Console()]
})
logger.log({
level: 'info',
message: 'What time is the testing at?'
});
// Outputs:
// { level: 'info',
// message: 'What time is the testing at?',
// label: 'right meow!',
// timestamp: '2017-09-30T03:57:26.875Z' }
The log
method provides the string interpolation using util.format. It
must be enabled using format.splat()
.
Below is an example that defines a format with string interpolation of
messages using format.splat
and then serializes the entire info
message
using format.simple
.
const { createLogger, format, transports } = require('winston');
const logger = createLogger({
format: format.combine(
format.splat(),
format.simple()
),
transports: [new transports.Console()]
});
// info: test message my string {}
logger.log('info', 'test message %s', 'my string');
// info: test message 123 {}
logger.log('info', 'test message %d', 123);
// info: test message first second {number: 123}
logger.log('info', 'test message %s, %s', 'first', 'second', { number: 123 });
If you wish to filter out a given info
Object completely when logging then
simply return a falsey value.
const { createLogger, format, transports } = require('winston');
// Ignore log messages if they have { private: true }
const ignorePrivate = format((info, opts) => {
if (info.private) { return false; }
return info;
});
const logger = createLogger({
format: format.combine(
ignorePrivate(),
format.json()
),
transports: [new transports.Console()]
});
// Outputs: {"level":"error","message":"Public error to share"}
logger.log({
level: 'error',
message: 'Public error to share'
});
// Messages with { private: true } will not be written when logged.
logger.log({
private: true,
level: 'error',
message: 'This is super secret - hide it.'
});
Use of format.combine
will respect any falsey values return and stop
evaluation of later formats in the series. For example:
const { format } = require('winston');
const { combine, timestamp, label } = format;
const willNeverThrow = format.combine(
format(info => { return false })(), // Ignores everything
format(info => { throw new Error('Never reached') })()
);
Formats are prototypal objects (i.e. class instances) that define a single
method: transform(info, opts)
and return the mutated info
:
info
: an object representing the log message.opts
: setting specific to the current instance of the format.
They are expected to return one of two things:
- An
info
Object representing the modifiedinfo
argument. Object references need not be preserved if immutability is preferred. All current built-in formats considerinfo
mutable, but [immutablejs] is being considered for future releases. - A falsey value indicating that the
info
argument should be ignored by the caller. (See: Filteringinfo
Objects) below.
winston.format
is designed to be as simple as possible. To define a new
format, simply pass it a transform(info, opts)
function to get a new
Format
.
The named Format
returned can be used to create as many copies of the given
Format
as desired:
const { format } = require('winston');
const volume = format((info, opts) => {
if (opts.yell) {
info.message = info.message.toUpperCase();
} else if (opts.whisper) {
info.message = info.message.toLowerCase();
}
return info;
});
// `volume` is now a function that returns instances of the format.
const scream = volume({ yell: true });
console.dir(scream.transform({
level: 'info',
message: `sorry for making you YELL in your head!`
}, scream.options));
// {
// level: 'info'
// message: 'SORRY FOR MAKING YOU YELL IN YOUR HEAD!'
// }
// `volume` can be used multiple times to create different formats.
const whisper = volume({ whisper: true });
console.dir(whisper.transform({
level: 'info',
message: `WHY ARE THEY MAKING US YELL SO MUCH!`
}, whisper.options));
// {
// level: 'info'
// message: 'why are they making us yell so much!'
// }
Logging levels in winston
conform to the severity ordering specified by
RFC5424: severity of all levels is assumed to be numerically ascending
from most important to least important.
Each level
is given a specific integer priority. The higher the priority the
more important the message is considered to be, and the lower the
corresponding integer priority. For example, as specified exactly in RFC5424
the syslog
levels are prioritized from 0 to 7 (highest to lowest).
{
emerg: 0,
alert: 1,
crit: 2,
error: 3,
warning: 4,
notice: 5,
info: 6,
debug: 7
}
Similarly, npm
logging levels are prioritized from 0 to 6 (highest to
lowest):
{
error: 0,
warn: 1,
info: 2,
http: 3,
verbose: 4,
debug: 5,
silly: 6
}
If you do not explicitly define the levels that winston
should use, the
npm
levels above will be used.
Setting the level for your logging message can be accomplished in one of two ways. You can pass a string representing the logging level to the log() method or use the level specified methods defined on every winston Logger.
//
// Any logger instance
//
logger.log('silly', "127.0.0.1 - there's no place like home");
logger.log('debug', "127.0.0.1 - there's no place like home");
logger.log('verbose', "127.0.0.1 - there's no place like home");
logger.log('info', "127.0.0.1 - there's no place like home");
logger.log('warn', "127.0.0.1 - there's no place like home");
logger.log('error', "127.0.0.1 - there's no place like home");
logger.info("127.0.0.1 - there's no place like home");
logger.warn("127.0.0.1 - there's no place like home");
logger.error("127.0.0.1 - there's no place like home");
//
// Default logger
//
winston.log('info', "127.0.0.1 - there's no place like home");
winston.info("127.0.0.1 - there's no place like home");
winston
allows you to define a level
property on each transport which
specifies the maximum level of messages that a transport should log. For
example, using the syslog
levels you could log only error
messages to the
console and everything info
and below to a file (which includes error
messages):
const logger = winston.createLogger({
levels: winston.config.syslog.levels,
transports: [
new winston.transports.Console({ level: 'error' }),
new winston.transports.File({
filename: 'combined.log',
level: 'info'
})
]
});
You may also dynamically change the log level of a transport:
const transports = {
console: new winston.transports.Console({ level: 'warn' }),
file: new winston.transports.File({ filename: 'combined.log', level: 'error' })
};
const logger = winston.createLogger({
transports: [
transports.console,
transports.file
]
});
logger.info('Will not be logged in either transport!');
transports.console.level = 'info';
transports.file.level = 'info';
logger.info('Will be logged in both transports!');
winston
supports customizable logging levels, defaulting to npm style
logging levels. Levels must be specified at the time of creating your logger.
In addition to the predefined npm
, syslog
, and cli
levels available in
winston
, you can also choose to define your own:
const myCustomLevels = {
levels: {
foo: 0,
bar: 1,
baz: 2,
foobar: 3
},
colors: {
foo: 'blue',
bar: 'green',
baz: 'yellow',
foobar: 'red'
}
};
const customLevelLogger = winston.createLogger({
levels: myCustomLevels.levels
});
customLevelLogger.foobar('some foobar level-ed message');
Although there is slight repetition in this data structure, it enables simple encapsulation if you do not want to have colors. If you do wish to have colors, in addition to passing the levels to the Logger itself, you must make winston aware of them:
winston.addColors(myCustomLevels.colors);
This enables loggers using the colorize
formatter to appropriately color and style
the output of custom levels.
Additionally, you can also change background color and font style. For example,
baz: 'italic yellow',
foobar: 'bold red cyanBG'
Possible options are below.
-
Font styles:
bold
,dim
,italic
,underline
,inverse
,hidden
,strikethrough
. -
Font foreground colors:
black
,red
,green
,yellow
,blue
,magenta
,cyan
,white
,gray
,grey
. -
Background colors:
blackBG
,redBG
,greenBG
,yellowBG
,blueBG
magentaBG
,cyanBG
,whiteBG
To colorize the standard logging level add
winston.format.combine(
winston.format.colorize(),
winston.format.json()
);
where winston.format.json()
is whatever other formatter you want to use. The colorize
formatter must come before any formatters adding text you wish to color.
There are several core transports included in winston
, which leverage the
built-in networking and file I/O offered by Node.js core. In addition, there
are additional transports written by members of the community.
It is possible to use multiple transports of the same type e.g.
winston.transports.File
when you construct the transport.
const logger = winston.createLogger({
transports: [
new winston.transports.File({
filename: 'combined.log',
level: 'info'
}),
new winston.transports.File({
filename: 'errors.log',
level: 'error'
})
]
});
If you later want to remove one of these transports you can do so by using the transport itself. e.g.:
const combinedLogs = logger.transports.find(transport => {
return transport.filename === 'combined.log'
});
logger.remove(combinedLogs);
Adding a custom transport is easy. All you need to do is accept any options
you need, implement a log() method, and consume it with winston
.
const Transport = require('winston-transport');
const util = require('util');
//
// Inherit from `winston-transport` so you can take advantage
// of the base functionality and `.exceptions.handle()`.
//
module.exports = class YourCustomTransport extends Transport {
constructor(opts) {
super(opts);
//
// Consume any custom options here. e.g.:
// - Connection information for databases
// - Authentication information for APIs (e.g. loggly, papertrail,
// logentries, etc.).
//
}
log(info, callback) {
setImmediate(() => {
this.emit('logged', info);
});
// Perform the writing to the remote service
callback();
}
};
As every transport inherits from winston-transport, it's possible to set a custom format and a custom log level on each transport separately:
const logger = winston.createLogger({
transports: [
new winston.transports.File({
filename: 'error.log',
level: 'error',
format: winston.format.json()
}),
new winston.transports.Http({
level: 'warn',
format: winston.format.json()
}),
new winston.transports.Console({
level: 'info',
format: winston.format.combine(
winston.format.colorize(),
winston.format.simple()
)
})
]
});
With winston
, it is possible to catch and log uncaughtException
events
from your process. With your own logger instance you can enable this behavior
when it's created or later on in your applications lifecycle:
const { createLogger, transports } = require('winston');
// Enable exception handling when you create your logger.
const logger = createLogger({
transports: [
new transports.File({ filename: 'combined.log' })
],
exceptionHandlers: [
new transports.File({ filename: 'exceptions.log' })
]
});
// Or enable it later on by adding a transport or using `.exceptions.handle`
const logger = createLogger({
transports: [
new transports.File({ filename: 'combined.log' })
]
});
// Call exceptions.handle with a transport to handle exceptions
logger.exceptions.handle(
new transports.File({ filename: 'exceptions.log' })
);
If you want to use this feature with the default logger, simply call
.exceptions.handle()
with a transport instance.
//
// You can add a separate exception logger by passing it to `.exceptions.handle`
//
winston.exceptions.handle(
new winston.transports.File({ filename: 'path/to/exceptions.log' })
);
//
// Alternatively you can set `handleExceptions` to true when adding transports
// to winston.
//
winston.add(new winston.transports.File({
filename: 'path/to/combined.log',
handleExceptions: true
}));
By default, winston will exit after logging an uncaughtException. If this is
not the behavior you want, set exitOnError = false
const logger = winston.createLogger({ exitOnError: false });
//
// or, like this:
//
logger.exitOnError = false;
When working with custom logger instances, you can pass in separate transports
to the exceptionHandlers
property or set handleExceptions
on any
transport.
const logger = winston.createLogger({
transports: [
new winston.transports.File({ filename: 'path/to/combined.log' })
],
exceptionHandlers: [
new winston.transports.File({ filename: 'path/to/exceptions.log' })
]
});
const logger = winston.createLogger({
transports: [
new winston.transports.Console({
handleExceptions: true
})
],
exitOnError: false
});
The exitOnError
option can also be a function to prevent exit on only
certain types of errors:
function ignoreEpipe(err) {
return err.code !== 'EPIPE';
}
const logger = winston.createLogger({ exitOnError: ignoreEpipe });
//
// or, like this:
//
logger.exitOnError = ignoreEpipe;
With winston
, it is possible to catch and log uncaughtRejection
events
from your process. With your own logger instance you can enable this behavior
when it's created or later on in your applications lifecycle:
const { createLogger, transports } = require('winston');
// Enable rejection handling when you create your logger.
const logger = createLogger({
transports: [
new transports.File({ filename: 'combined.log' })
],
rejectionHandlers: [
new transports.File({ filename: 'rejections.log' })
]
});
// Or enable it later on by adding a transport or using `.rejections.handle`
const logger = createLogger({
transports: [
new transports.File({ filename: 'combined.log' })
]
});
// Call rejections.handle with a transport to handle rejections
logger.rejections.handle(
new transports.File({ filename: 'rejections.log' })
);
If you want to use this feature with the default logger, simply call
.rejections.handle()
with a transport instance.
//
// You can add a separate rejection logger by passing it to `.rejections.handle`
//
winston.rejections.handle(
new winston.transports.File({ filename: 'path/to/rejections.log' })
);
//
// Alternatively you can set `handleRejections` to true when adding transports
// to winston.
//
winston.add(new winston.transports.File({
filename: 'path/to/combined.log',
handleRejections: true
}));
In addition to logging messages and metadata, winston
also has a simple
profiling mechanism implemented for any logger:
//
// Start profile of 'test'
//
logger.profile('test');
setTimeout(function () {
//
// Stop profile of 'test'. Logging will now take place:
// '17 Jan 21:00:00 - info: test duration=1000ms'
//
logger.profile('test');
}, 1000);
Also you can start a timer and keep a reference that you can call .done()
on:
// Returns an object corresponding to a specific timing. When done
// is called the timer will finish and log the duration. e.g.:
//
const profiler = logger.startTimer();
setTimeout(function () {
profiler.done({ message: 'Logging message' });
}, 1000);
All profile messages are set to 'info' level by default, and both message and
metadata are optional. For individual profile messages, you can override the default log level by supplying a metadata object with a level
property:
logger.profile('test', { level: 'debug' });
winston
supports querying of logs with Loggly-like options. See Loggly
Search API. Specifically:
File
, Couchdb
, Redis
, Loggly
, Nssocket
, and Http
.
const options = {
from: new Date() - (24 * 60 * 60 * 1000),
until: new Date(),
limit: 10,
start: 0,
order: 'desc',
fields: ['message']
};
//
// Find items logged between today and yesterday.
//
logger.query(options, function (err, results) {
if (err) {
/* TODO: handle me */
throw err;
}
console.log(results);
});
Streaming allows you to stream your logs back from your chosen transport.
//
// Start at the end.
//
winston.stream({ start: -1 }).on('log', function(log) {
console.log(log);
});
The default logger is accessible through the winston
module directly. Any
method that you could call on an instance of a logger is available on the
default logger:
const winston = require('winston');
winston.log('info', 'Hello distributed log files!');
winston.info('Hello again distributed logs');
winston.level = 'debug';
winston.log('debug', 'Now my debug messages are written to console!');
By default, no transports are set on the default logger. You must
add or remove transports via the add()
and remove()
methods:
const files = new winston.transports.File({ filename: 'combined.log' });
const console = new winston.transports.Console();
winston.add(console);
winston.add(files);
winston.remove(console);
Or do it with one call to configure():
winston.configure({
transports: [
new winston.transports.File({ filename: 'somefile.log' })
]
});
For more documentation about working with each individual transport supported
by winston
see the winston
Transports document.
Often it is useful to wait for your logs to be written before exiting the
process. Each instance of winston.Logger
is also a [Node.js stream]. A
finish
event will be raised when all logs have flushed to all transports
after the stream has been ended.
const transport = new winston.transports.Console();
const logger = winston.createLogger({
transports: [transport]
});
logger.on('finish', function (info) {
// All `info` log messages has now been logged
});
logger.info('CHILL WINSTON!', { seriously: true });
logger.end();
It is also worth mentioning that the logger also emits an 'error' event if an error occurs within the logger itself which you should handle or suppress if you don't want unhandled exceptions:
//
// Handle errors originating in the logger itself
//
logger.on('error', function (err) { /* Do Something */ });
Often in larger, more complex, applications it is necessary to have multiple
logger instances with different settings. Each logger is responsible for a
different feature area (or category). This is exposed in winston
in two
ways: through winston.loggers
and instances of winston.Container
. In fact,
winston.loggers
is just a predefined instance of winston.Container
:
const winston = require('winston');
const { format } = winston;
const { combine, label, json } = format;
//
// Configure the logger for `category1`
//
winston.loggers.add('category1', {
format: combine(
label({ label: 'category one' }),
json()
),
transports: [
new winston.transports.Console({ level: 'silly' }),
new winston.transports.File({ filename: 'somefile.log' })
]
});
//
// Configure the logger for `category2`
//
winston.loggers.add('category2', {
format: combine(
label({ label: 'category two' }),
json()
),
transports: [
new winston.transports.Http({ host: 'localhost', port:8080 })
]
});
Now that your loggers are setup, you can require winston in any file in your application and access these pre-configured loggers:
const winston = require('winston');
//
// Grab your preconfigured loggers
//
const category1 = winston.loggers.get('category1');
const category2 = winston.loggers.get('category2');
category1.info('logging to file and console transports');
category2.info('logging to http transport');
If you prefer to manage the Container
yourself, you can simply instantiate one:
const winston = require('winston');
const { format } = winston;
const { combine, label, json } = format;
const container = new winston.Container();
container.add('category1', {
format: combine(
label({ label: 'category one' }),
json()
),
transports: [
new winston.transports.Console({ level: 'silly' }),
new winston.transports.File({ filename: 'somefile.log' })
]
});
const category1 = container.get('category1');
category1.info('logging to file and console transports');
npm install winston
yarn add winston
All of the winston tests are written with mocha
, nyc
, and
assume
. They can be run with npm
.
npm test