logger - Backendjs Documentation

logger

↓ Members.

↓ Methods.

module:logger

Description:

Logging utility

Default mode is to use util.inspect and output to stdout

Syslog mode can log to local or remote syslog with customizable facility and level

JSON mode will output an object with predefined properties first then the rest will be put inside the data array
```
{"level":"LOG","date":"2026-05-10T18:22:16.066Z","now":1778437336066,"role":"node","pid":71942, "data": ["shutdownServer:", "api", "node", "server", "closed"] }
```
AsyncLocalStorage is available as logger.als and can be used to output contexts
```
logger.als.run({ reqId: "123" }, (req, res) => {
    ...
    getUser(req.params.id, (err) => {
        if (err) logger.error("failed", req.params.id, err);
    })
})
```

Source:

logger.js, line 57

Example

logger.setLevel("info")
logger.log("log")             // visible
logger.info("info")           // visible
logger.debug("debug")         // not visible
logger.error("error")         // visible

logger.setLevel("debug")
logger.debug("debug")         // visible

logger.setLevel("info")
logger.setDebugFilter("custom")
logger.debug("debug")         // still not visible
logger.debug("custom")        // visible

Members

(static) als :AsyncLocalStorage

Description:

if set the current store will be added to the log arguments

Source:

logger.js, line 121

(static) date :string

Description:

default date format is $BKJS_LOG_DATE or local or iso or utc or none

Source:

logger.js, line 106

Default Value:

>iso

(static) filters :object

Description:

debugging filters enabled, can be set via $BKJS_LOG_FILTER

Source:

logger.js, line 73

(static) inspectArgs :object

Description:

defaults for util.inspect

Source:

logger.js, line 96

(static) json :boolean

Description:

if true the outout will be a JSON object

Source:

logger.js, line 91

Default Value:

>false

(static) level :int

Description:

current logging level, can be set via $BKJS_LOG_LEVEL

Source:

logger.js, line 65

Default Value:

>0(WARN)

(static) levels :object

Description:

levels sorted by priorities: ERROR, WARN, LOG, INFO, DEBUG, DEV

Source:

logger.js, line 68

(static) oneline :boolean

Description:

if true newlines will be replaced with spaces,

Source:

logger.js, line 85

Default Value:

>false

(static) pid :string

Description:

pid is $BKJS_LOG_PID or the current process pid

Source:

logger.js, line 112

Default Value:

>process.pid

(static) role :string

Description:

default role is $BKJS_LOG_ROLE if present

Source:

logger.js, line 118

(static) separator :string

Description:

concat argumenrs with this separator @default

Source:

logger.js, line 79

Default Value:

>space

(static) tag :string

Description:

default tag is $BKJS_LOG_TAG if present

Source:

logger.js, line 115

Methods

(static) debug(…args)

Description:

Log with DEBUG level, enabled debug filter will be logged if matched

Source:

logger.js, line 457

Parameters:

Name	Type	Attributes	Description
`args`	any	<repeatable>

(static) dev(…args)

Description:

Log with DEV level

Source:

logger.js, line 470

Parameters:

Name	Type	Attributes	Description
`args`	any	<repeatable>

(static) dump()

Description:

Raw output using util.format

Source:

logger.js, line 506

(static) error(…args)

Description:

Log with ERROR level

Source:

logger.js, line 483

Parameters:

Name	Type	Attributes	Description
`args`	any	<repeatable>

(static) info(…args)

Description:

Log with INFO level

Source:

logger.js, line 431

Parameters:

Name	Type	Attributes	Description
`args`	any	<repeatable>

(static) inspect(level, args) → {string}

Description:

Called by logger methods to perform input formatting and cleaning, calls default or installed inspector

Source:

logger.js, line 565

Parameters:

Name	Type	Description
`level`	string	current logging level
`args`	Array.<any>	items to output

Returns:

Type	Description
string	formatted output

(static) log(…args)

Description:

Log with LOG level

Source:

logger.js, line 419

Parameters:

Name	Type	Attributes	Description
`args`	any	<repeatable>

(static) logger(level, …args)

Description:

A generic logger method, safe, first arg is supposed to be a logging level, if not valid the error level is used

Source:

logger.js, line 529

Parameters:

Name	Type	Attributes	Description
`level`	string		logging level, can be one of the default levels or custom one registered with {registerLevel}
`args`	any	<repeatable>	arguments to log

(static) none(…args)

Description:

Log with NONE level, no-op

Source:

logger.js, line 495

Parameters:

Name	Type	Attributes	Description
`args`	any	<repeatable>

(static) registerLevel(level, callback, optionsopt)

Description:

Register a custom level handler, must be invoked via logger.logger only, if no handler registered for given level the whole message will be logger as an error. The custom handler is called in the context of the module which means the options are available inside the handler.

Source:

logger.js, line 202

Parameters:

Name	Type	Attributes	Description
`level`	string		custom log level
`callback`	function		call it for this level
`options`	Object	<optional>

(static) setDebugFilter(label, {function)

Description:

Enable debugging level for this label, if used with the same debugging level it will be printed regardless of the global level, a label is first argument to the logger.debug methods, it is used as is, usually the fist argument is the current function name with comma, like logger.debug("select:", name, args)

Source:

logger.js, line 372

Parameters:

Name	Type	Description
`label`	string	label(s) to debug, can be a comma separated list
`{function`		handler - can be a function to be used instead of regular logging, this is for rerouting some output to a custom console or for dumping the actual Javascript data without preformatting, most useful to use `console.log`

(static) setFile(file)

Description:

Redirect logging into a file, disables syslog

Source:

logger.js, line 218

Parameters:

Name	Type	Description
`file`	string

Example

logger.setFile('var/log/error.log')

(static) setInspect(inspect, inspectArgsopt)

Description:

Install a custom inspector with options

Source:

logger.js, line 182

Parameters:

Name	Type	Attributes	Description
`inspect`	function		function to output
`inspectArgs`	object	<optional>

(static) setLevel(level)

Description:

Set the output level, it can be a number or one of the supported level names, on invalid level then WARN is set

Source:

logger.js, line 358

Parameters:

Name	Type	Description
`level`	stream

(static) setOptions(options)

Description:

Special options for logger to override defaults, syslog options must start with syslog- For tag, date, pid values may refer to other env variables if start with $, like BKJS_LOG_TAG='$BKJS_TAG'

Source:

logger.js, line 298

Parameters:

Name Type Description

options

Object

Properties

Name	Type	Attributes	Description
`filter`	string	<optional>	debug filters
`level`	string	<optional>	set current level
`tag`	string	<optional>	syslog tag
`pid`	int	<optional>	process id
`date`	date	<optional>	date format: `local, iso, utc`
`oneline`	boolean	<optional>	replace newlines if true
`json`	boolean	<optional>	enable JSON mode, each entry will be an Array
`syslog-hostname`	string	<optional>	syslog hostname to use
`syslog-facility`	string	<optional>	syslog hostname to use
`syslog-bsd`	boolean	<optional>	syslog version
`syslog-rfc5424`	boolean	<optional>	syslog version
`syslog-rfc3164`	boolean	<optional>	syslog version

(static) setSyslog(facility)

Description:

Enable or close syslog mode

Source:

logger.js, line 244

Parameters:

Name	Type	Description
`facility`	int \| string	syslog facility as a number or remote syslog server:, nullish value will disable syslog

Example

logger.setSyslog('unix://')
logger.setSyslog('udp://host?tag=app')
logger.setSyslog('tcp://host:514?facility=LOG_LOCAL0')

// Back to console output
logger.setSyslog()

(static) trace()

Description:

Print stack backtrace as error

Source:

logger.js, line 516

(static) warn(…args)

Description:

Log with WARN level

Source:

logger.js, line 444

Parameters:

Name	Type	Attributes	Description
`args`	any	<repeatable>