# Table of Contents

+ [pino](#constructor)
+ [pino.pretty](#pretty)
+ [Logger Instance](#logger)
  * [.pino](#version)
  * [.child](#child)
  * [.level](#level)
  * [.fatal](#fatal)
  * [.error](#error)
  * [.warn](#warn)
  * [.info](#info)
  * [.debug](#debug)
  * [.trace](#trace)
  * [.flush](#flush)
  * [.addLevel](#addLevel)
  * [.levelVal](#levelVal)
  * [level-change (event)](#level-change)
  * [.levels.values](#levelValues)
  * [.levels.labels](#levelLabels)
  * [.isLevelEnabled](#isLevelEnabled)
  * [LOG_VERSION](#log_version)
  * [.stdSerializers](#stdSerializers)
    + [.req](#reqSerializer)
    + [.res](#resSerializer)
    + [.err](#errSerializer)
    + [.wrapRequestSerializer](#wrapReq)
    + [.wrapResponseSerializers](#wrapRes)
  + [.stdTimeFunctions](#stdTimeFunctions)
    + [.epochTime](#epochTimeFunction)
    + [.unixTime](#unixTimeFunction)
    + [.slowTime](#slowTimeFunction)
    + [.nullTime](#nullTimeFunction)
+ [Metadata Support](#metadata)

# module.exports

<a id="constructor"></a>
## .pino([options], [stream])

### Parameters:
+ `options` (object):
  * `safe` (boolean): avoid error caused by circular references in the object tree.
    Default: `true`.
  * `name` (string): the name of the logger. Default: `undefined`.
  * `serializers` (object): an object containing functions for custom serialization
    of objects. These functions should return an JSONifiable object and they
    should never throw. When logging an object, each top-level property matching the exact key of a serializer
    will be serialized using the defined serializer.

    Alternatively, it is possible to register a serializer under the key `Symbol.for('pino.*')` which will act upon the complete log object, i.e. every property.
  * `timestamp` (boolean|function): Enables or disables the inclusion of a timestamp in the
    log message. If a function is supplied, it must synchronously return a JSON string
    representation of the time, e.g. `,"time":1493426328206 (which is the default).
    If set to `false`, no timestamp will be included in the output.
    See [stdTimeFunctions](#stdTimeFunctions) for a set of available functions
    for passing in as a value for this option. Caution: any sort of formatted
    time will significantly slow down Pino's performance.
  * `slowtime` (boolean): Outputs ISO time stamps (`'2016-03-09T15:18:53.889Z'`)
     instead of Epoch time stamps (`1457536759176`). **WARNING**: This option
     carries a 25% performance drop. We recommend using default Epoch timestamps
     and transforming logs after if required. The `pino -t` command will do this
     for you (see [CLI](cli.md)). Default: `false`.
     **Deprecation**: this option is scheduled to be removed in Pino 5.0.0. Use
     `timestamp: pino.stdTimeFunctions.slowTime` instead.
  * `extreme` (boolean): Enables extreme mode, yields an additional 60% performance
    (from 250ms down to 100ms per 10000 ops). There are trade-off's should be
    understood before usage. See [Extreme mode explained](extreme.md). Default: `false`.
  * `level` (string): one of `'fatal'`, `'error'`, `'warn'`, `'info`', `'debug'`,
    `'trace'`; also `'silent'` is supported to disable logging. Any other value
    defines a custom level and requires supplying a level value via `levelVal`.
    Default: 'info'.
  * `levelVal` (integer): when defining a custom log level via `level`, set to an
    integer value to define the new level. Default: `undefined`.
  * `messageKey` (string): the string key for the 'message' in the JSON object. Default `msg`.
  * `prettyPrint` (boolean|object): enables [pino.pretty](#pretty). This is intended for non-production
    configurations. This may be set to a configuration object as outlined in [pino.pretty](#pretty). Default: `false`.
  * `onTerminated` (function): this function will be invoked during process shutdown when `extreme` is set to `true`.
    The signature of the function is `onTerminated(eventName, err)`. If you do not specify a function, Pino will
    invoke `process.exit(0)` when no error has occurred, and `process.exit(1)` otherwise. If you do specify a function,
    it is up to you to terminate the process; you **must** perform only synchronous operations at this point.
    See [Extreme mode explained](extreme.md) for more detail.
  * `enabled` (boolean): enables logging. Default: `true`
  * `browser` (Object): browser only, may have `asObject` and `write` keys, see [Pino in the Browser](/README.md#browser)
  * `base` (Object): key-value object added as child logger to each log line. If set to `null` the `base` child logger is not added . Default:
    * `pid` (process.pid)
    * `hostname` (os.hostname)
    * `name` of logger if supplied as option
  * `crlf` (boolean): logs newline delimited JSON with `\r\n` instead of `\n`. Default: `false`.
+ `stream` (Writable): a writable stream where the logs will be written.
  It can also receive some log-line [metadata](#metadata), if the
  relative protocol is enabled. Default: `process.stdout`

### Example:
```js
'use strict'

var pino = require('pino')
var logger = pino({
  name: 'myapp',
  safe: true,
  serializers: {
    req: pino.stdSerializers.req,
    res: pino.stdSerializers.res
  }
})
```
### Discussion:
Returns a new [logger](#logger) instance.

<a id="pretty"></a>
## .pretty([options])

### Parameters:
+ `options` (object):
  * `timeTransOnly` (boolean): if set to `true`, it will only covert the unix
  timestamp to ISO 8601 date format, and reserialize the JSON (equivalent to `pino -t`).
  * `formatter` (function): a custom function to format the line. It's passed 2 arguments,
  JSON object log data and an options object
  that [exposes utility functions](https://github.com/pinojs/pino/blob/master/pretty.js#L110).
  It should return a string value.
  * `levelFirst` (boolean): if set to `true`, it will print the name of the log
  level as the first field in the log line. Default: `false`.
  * `messageKey` (string): the key in the JSON object to use as the highlighted
  message. Default: `msg`.
  * `forceColor` (boolean): if set to `true`, will add color information to the formatted output
  message. Default: `false`.
  * `crlf` (boolean): emit `\r\n` instead of `\n`. Default: `false`.
  * `errorLikeObjectKeys` (array): error-like objects containing stack traces that should be prettified. Default: `['err', 'error']`.

### Example:
```js
'use strict'

var pino = require('pino')
var pretty = pino.pretty()
pretty.pipe(process.stdout)
var log = pino({
  name: 'app',
  safe: true
}, pretty)

log.child({ widget: 'foo' }).info('hello')
log.child({ widget: 'bar' }).warn('hello 2')
```

### Discussion:
Provides access to the [CLI](cli.md) log prettifier as an API.

This can also be enabled via the [constructor](#constructor) by setting the
`prettyPrint` option to either `true` or a configuration object described
in this section.

<a id="logger"></a>
# Logger

<a id="version"></a>
## .pino

Exposes the current version of Pino.

### Example:
```js
var log = require('pino')()
if ('pino' in child) console.log(`pino version: ${log.pino}`)
```

<a id="child"></a>
## .child(bindings)

### Parameters:
+ `bindings` (object): an object of key-value pairs to include in log lines
  as properties.

### Example:
```js
logger.child({ a: 'property' }).info('hello child!')
// generates
// {"pid":46497,"hostname":"MacBook-Pro-di-Matteo.local","level":30,"msg":"hello child!","time":1458124707120,"v":0,"a":"property"}
```

### Discussion:
Creates a child logger, setting all key-value pairs in `bindings` as properties
in the log lines. All serializers will be applied to the given pair.

Child loggers use the same output stream as the parent and inherit
the current log level of the parent at the time they are spawned.

From v2.x.x the log level of a child is mutable (whereas in
v1.x.x it was immutable), and can be set independently of the parent.
If a `level` property is present in the object passed to `child` it will
override the child logger level.

For example:

```
var logger = pino()
logger.level = 'error'
logger.info('nope') //does not log
var child = logger.child({foo: 'bar'})
child.info('nope again') //does not log
child.level = 'info'
child.info('hooray') //will log
logger.info('nope nope nope') //will not log, level is still set to error
logger.child({ foo: 'bar', level: 'debug' }).debug('debug!')
```

Child loggers inherit the serializers from the parent logger but it is
possible to override them.

For example:

```
var pino = require('./pino')

var customSerializers = {
  test: function () {
    return 'this is my serializer'
  }
}
var child = pino().child({serializers: customSerializers})

child.info({test: 'should not show up'})
```

Will produce the following output:

```
{"pid":7971,"hostname":"mycomputer.local","level":30,"time":1469488147985,"test":"this is my serializer","v":1}
```

Also from version 2.x.x we can spawn child loggers from child loggers, for instance:

```
var logger = pino()
var child = logger.child({father: true})
var childChild = child.child({baby: true})
```

Child logger creation is fast:

```
benchBunyanCreation*10000: 1291.332ms
benchBoleCreation*10000: 1630.542ms
benchPinoCreation*10000: 352.330ms
benchPinoExtremeCreation*10000: 102.282ms
```

Logging through a child logger has little performance penalty:

```
benchBunyanChild*10000: 1343.933ms
benchBoleChild*10000: 1605.969ms
benchPinoChild*10000: 334.573ms
benchPinoExtremeChild*10000: 152.792ms
```

Spawning children from children has negligible overhead:

```
benchBunyanChildChild*10000: 1397.202ms
benchPinoChildChild*10000: 338.930ms
benchPinoExtremeChildChild*10000: 150.143ms
```

<a id="level"></a>
## .level

### Example:
```
logger.level = 'info'
```

### Discussion:

Set this property to the desired logging level. In order of priority, available
levels are:

  1. <a href="#fatal">`'fatal'`</a>
  2. <a href="#error">`'error'`</a>
  3. <a href="#warn">`'warn'`</a>
  4. <a href="#info">`'info'`</a>
  5. <a href="#debug">`'debug'`</a>
  6. <a href="#trace">`'trace'`</a>

The logging level is a *minimum* level. For instance if `logger.level` is
`'info'` then all `'fatal'`, `'error'`, `'warn'`, and `'info'` logs will be enabled.

You can pass `'silent'` to disable logging.

<a id="fatal"></a>
## .fatal([obj], msg, [...])

### Parameters:
+ `obj` (object): object to be serialized
+ `msg` (string): the log message to write
+ `...` (*): format string values when `msg` is a format string

### Discussion:
Log at `'fatal'` level the given `msg`. The `msg` may contain up to 10
[format string tokens][formatstrs] (given that the method accetps up to 11
arguments total). The subsequent parameters passed will be used to fill in these
placeholder tokens with the associated value. Any extra parameters will be
silently ignored. For example, `log.fatal('%s', 'a', 'b')` will only log the
string `a` and ignore the `'b'` parameter.

If the first argument is an object, all its properties will be included in the
JSON line. The number of available format string tokens and associated
parameters will be reduced accodringly.

[formatstrs]: https://nodejs.org/dist/latest-v8.x/docs/api/util.html#util_util_format_format_args

<a id="error"></a>
## .error([obj], msg, [...])

### Parameters:
+ `obj` (object): object to be serialized
+ `msg` (string): the log message to write
+ `...` (*): format string values when `msg` is a format string

### Discussion:
Log at `'error'` level the given `msg`. The `msg` may contain up to 10
[format string tokens][formatstrs] (given that the method accetps up to 11
arguments total). The subsequent parameters passed will be used to fill in these
placeholder tokens with the associated value. Any extra parameters will be
silently ignored. For example, `log.error('%s', 'a', 'b')` will only log the
string `a` and ignore the `'b'` parameter.

If the first argument is an object, all its properties will be included in the
JSON line. The number of available format string tokens and associated
parameters will be reduced accodringly.

<a id="warn"></a>
## .warn([obj], msg, [...])

### Parameters:
+ `obj` (object): object to be serialized
+ `msg` (string): the log message to write
+ `...` (*): format string values when `msg` is a format string

### Discussion:
Log at `'warn'` level the given `msg`. The `msg` may contain up to 10
[format string tokens][formatstrs] (given that the method accetps up to 11
arguments total). The subsequent parameters passed will be used to fill in these
placeholder tokens with the associated value. Any extra parameters will be
silently ignored. For example, `log.warn('%s', 'a', 'b')` will only log the
string `a` and ignore the `'b'` parameter.

If the first argument is an object, all its properties will be included in the
JSON line. The number of available format string tokens and associated
parameters will be reduced accodringly.

<a id="info"></a>
## .info([obj], msg, [...])

### Parameters:
+ `obj` (object): object to be serialized
+ `msg` (string): the log message to write
+ `...` (*): format string values when `msg` is a format string

### Discussion:
Log at `'info'` level the given `msg`. The `msg` may contain up to 10
[format string tokens][formatstrs] (given that the method accetps up to 11
arguments total). The subsequent parameters passed will be used to fill in these
placeholder tokens with the associated value. Any extra parameters will be
silently ignored. For example, `log.info('%s', 'a', 'b')` will only log the
string `a` and ignore the `'b'` parameter.

If the first argument is an object, all its properties will be included in the
JSON line. The number of available format string tokens and associated
parameters will be reduced accodringly.

<a id="debug"></a>
## .debug([obj], msg, [...])

### Parameters:
+ `obj` (object): object to be serialized
+ `msg` (string): the log message to write
+ `...` (*): format string values when `msg` is a format string

### Discussion:
Log at `'debug'` level the given `msg`. The `msg` may contain up to 10
[format string tokens][formatstrs] (given that the method accetps up to 11
arguments total). The subsequent parameters passed will be used to fill in these
placeholder tokens with the associated value. Any extra parameters will be
silently ignored. For example, `log.debug('%s', 'a', 'b')` will only log the
string `a` and ignore the `'b'` parameter.

If the first argument is an object, all its properties will be included in the
JSON line. The number of available format string tokens and associated
parameters will be reduced accodringly.

<a id="trace"></a>
## .trace([obj], msg, [...])

### Parameters:
+ `obj` (object): object to be serialized
+ `msg` (string): the log message to write
+ `...` (*): format string values when `msg` is a format string

### Discussion:
Log at `'trace'` level the given `msg`. The `msg` may contain up to 10
[format string tokens][formatstrs] (given that the method accetps up to 11
arguments total). The subsequent parameters passed will be used to fill in these
placeholder tokens with the associated value. Any extra parameters will be
silently ignored. For example, `log.trace('%s', 'a', 'b')` will only log the
string `a` and ignore the `'b'` parameter.

If the first argument is an object, all its properties will be included in the
JSON line. The number of available format string tokens and associated
parameters will be reduced accodringly.

<a id="flush"></a>
## .flush()

### Discussion:
Flushes the content of the buffer in [extreme mode](extreme.md). It has no effect if
extreme mode is not enabled.

<a id="addLevel"></a>
## .addLevel(name, lvl)

### Parameters:
+ `name` (string): defines the method name of the new level
+ `lvl` (integer): value for the level, e.g. `35` is between `info` and `warn`

### Example:
```js
var pino = require('pino')
var log = pino()
log.addLevel('myLevel', 35)
log.level = 'myLevel'
log.myLevel('a message')
```

### Discussion:
Defines a new level on the logger instance.
Returns `true` on success and `false` if there was a conflict (level name or
number already exists).

When using this method, the current level of the logger instance does not change.
You must adjust the level with the [level](#level) property after adding your
custom level.

If you need a custom level at construction, you can supply the `level` and
`levelVal` options:

```js
var pino = require('pino')
var log = pino({level: 'myLevel', levelVal: 35})
log.myLevel('a message')
```

The level is set to the custom level on construction, i.e. `log.level` does not
need to be set.

<a id="levelVal"></a>
## .levelVal

### Example:
```js
if (logger.levelVal === 30) {
  console.log('logger level is `info`')
}
```

### Discussion:
Returns the integer value for the logger instance's logging level.

<a id="level-change"></a>
## .on('level-change', fn)

### Example:
```js
var listener = function (lvl, val, prevLvl, prevVal) {
  console.log(lvl, val, prevLvl, prevVal)
}
logger.on('level-change', listener)
logger.level = 'trace' // trigger console message
logger.removeListener('level-change', listener)
logger.level = 'info' // no message, since listener was removed
```

### Discussion:
Registers a listener function that is triggered when the level is changed.

The listener is passed four arguments: `levelLabel`, `levelValue`,
`previousLevelLabel`, `previousLevelValue`.

**Note:** When browserified, this functionality will only be available if the
`events` module has been required elsewhere (e.g. if you're using streams
in the browser). This allows for a trade-off between bundle size and functionality.

<a id="levelValues"></a>
## .levels.values

### Example:
```js
pino.levels.values.error === 50 // true
```

### Discussion:
Returns the mappings of level names to their respective internal number
representation. This property is available as a static property or as an
instance property.

<a id="levelLabels"></a>
## .levels.labels

### Example:
```js
pino.levels.labels[50] === 'error' // true
```

### Discussion:
Returns the mappings of level internal level numbers to their string
representations. This property is available as a static property or as an
instance property.

<a id="isLevelEnabled"></a>
## .isLevelEnabled(logLevel)

### Example:
```js
if (logger.isLevelEnabled('debug')) logger.debug('conditional log')
```

### Discussion:
A utility method for determining if a given log level will write to the output
stream.

<a id="log_version"></a>
## .LOG_VERSION

### Discussion:
Read only. Holds the current log format version (as output in the `v`
property of each log record). This property is available as a static property
or as an instance property.

<a id="stdSerializers"></a>
## .stdSerializers

Available as a static property, the `stdSerializers` provide functions for
serializing objects common to many projects. The serializers are directly
imported from [pino-std-serializers](https://github.com/pinojs/pino-std-serializers).

<a id="reqSerializer"></a>
### .req

Generates a JSONifiable object from the HTTP `request` object passed to
the `createServer` callback of Node's HTTP server.

It returns an object in the form:

```js
{
  pid: 93535,
  hostname: 'your host',
  level: 30,
  msg: 'my request',
  time: '2016-03-07T12:21:48.766Z',
  v: 0,
  req: {
    method: 'GET',
    url: '/',
    headers: {
      host: 'localhost:50201',
      connection: 'close'
    },
    remoteAddress: '::ffff:127.0.0.1',
    remotePort: 50202
  }
}
```

<a id="resSerializer"></a>
### .res

Generates a JSONifiable object from the HTTP `response` object passed to
the `createServer` callback of Node's HTTP server.

It returns an object in the form:

```js
{
  pid: 93581,
  hostname: 'myhost',
  level: 30,
  msg: 'my response',
  time: '2016-03-07T12:23:18.041Z',
  v: 0,
  res: {
    statusCode: 200,
    header: 'HTTP/1.1 200 OK\r\nDate: Mon, 07 Mar 2016 12:23:18 GMT\r\nConnection: close\r\nContent-Length: 5\r\n\r\n'
  }
}
```

<a id="errSerializer"></a>
### .err

Serializes an `Error` object if passed in as an property.

```js
{
  "pid": 40510,
  "hostname": "MBP-di-Matteo",
  "level": 50,
  "msg": "an error",
  "time": 1459433282301,
  "v": 1,
  "type": "Error",
  "stack": "Error: an error\n    at Object.<anonymous> (/Users/matteo/Repositories/pino/example.js:16:7)\n    at Module._compile (module.js:435:26)\n    at Object.Module._extensions..js (module.js:442:10)\n    at Module.load (module.js:356:32)\n    at Function.Module._load (module.js:313:12)\n    at Function.Module.runMain (module.js:467:10)\n    at startup (node.js:136:18)\n    at node.js:963:3"
}
```

<a id="wrapReq"></a>
## .wrapRequestSerializer

Wraps the standard request serializer such that custom serializers can use
the newly serilized request. An example of using this function can be found
in the [pino-http][https://github.com/pinojs/pino-http] module.

<a id="wrapRes"></a>
## .wrapResponseSerializer

Wraps the standard response serializer such that custom serializers can use
the newly serilized response. An example of using this function can be found
in the [pino-http][https://github.com/pinojs/pino-http] module.

<a id="stdTimeFunctions"></a>
## .stdTimeFunctions

Available as a static property, the `stdTimeFunctions` provide functions for
generating the timestamp property in the log output. You can set the `timestamp`
option during initialization to one of these functions to adjust the output
format. Alternatively, you can specify your own time function.

A time function must synchronously return a string that would be a valid
component of a JSON string. For example, the default function returns
a string like `,"time":1493426328206`.

<a id="epochTimeFunction"></a>
### .epochTime

The default time function for Pino. Returns a string like `,"time":1493426328206`.

<a id="unixTimeFunction"></a>
### .unixTime

Returns a unix time in seconds, like `,"time":1493426328`.

<a id="slowTimeFunction"></a>
### .slowTime

Returns an ISO formatted string like `,"time":"2017-04-29T00:47:49.354Z". It is
highly recommended that you avoid this function. It incurs a significant
performance penalty.

<a id="nullTimeFunction"></a>
### .nullTime

Returns an empty string. This function is used when the `timestamp` option
is set to `false`.

<a id="metadata"></a>
# Metadata

A destination stream can have a property `stream[Symbol.for('needsMetadata')] = true`
to indicate that for every log line written, the following properties of the stream
should be set:

* the last logging level as `stream.lastLevel`
* the last logging message as `stream.lastMsg`
* the last logging object as `stream.lastObj`
* the last time as `stream.lastTime`, which will be the partial string returned
  by the time function.
* the last logger instance as `stream.lastLogger` (to support child
  loggers)

## Example

```js
var instance = pino({}, {
  [Symbol.for('needsMetadata')]: true,
  write: function (chunk) {
    console.log('lastLevel', this.lastLevel)
    console.log('lastMsg', this.lastMsg)
    console.log('lastObj', this.lastObj)
    console.log('lastLogger', this.lastLogger)
    console.log('line', chunk)
  }
})
```