# logform
A mutable object-based log format designed for chaining & objectMode streams.
``` js
const { format } = require('logform');
const alignedWithColorsAndTime = format.combine(
format.colorize(),
format.timestamp(),
format.align(),
format.printf(info => `${info.timestamp} ${info.level}: ${info.message}`)
);
```
- [`info` Objects](#info-objects)
- [Understanding formats](#understanding-formats)
- [Combining formats](#combining-formats)
- [Filtering `info` objects](#filtering-info-objects)
- [Formats](#formats)
- [Align](#align)
- [CLI](#cli)
- [Colorize](#colorize)
- [Combine](#combine)
- [Errors](#errors)
- [JSON](#json)
- [Label](#label)
- [Logstash](#logstash)
- [Metadata](#metadata)
- [PadLevels](#padlevels)
- [PrettyPrint](#prettyprint)
- [Printf](#printf)
- [Simple](#simple)
- [Splat](#splat)
- [Timestamp](#timestamp)
- [Uncolorize](#uncolorize)
## `info` Objects
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:
``` js
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.:
``` js
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 to `level` 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 by `splat()` format._
These Symbols are stored in another package: `triple-beam` so that all
consumers of `logform` can have the same Symbol reference. i.e.:
``` js
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
```
## Understanding formats
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 modified `info` argument. Object references need not be preserved if immutability is preferred. All current built-in formats consider `info` mutable, but [immutablejs] is being considered for future releases.
- **A falsey value** indicating that the `info` argument should be ignored by the caller. (See: [Filtering `info` Objects](#filtering-info-objects)) below.
`logform.format` is designed to be as simple as possible. To define a new format simple 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:
``` js
const { format } = require('logform');
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!'
// }
```
### Combining formats
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.
``` js
const { format } = require('logform');
const { combine, timestamp, label } = format;
const labelTimestamp = combine(
label({ label: 'right meow!' }),
timestamp()
);
const info = labelTimestamp.transform({
level: 'info',
message: 'What time is the testing at?'
});
console.dir(info);
// { level: 'info',
// message: 'What time is the testing at?',
// label: 'right meow!',
// timestamp: '2017-09-30T03:57:26.875Z' }
```
### Filtering `info` Objects
If you wish to filter out a given `info` Object completely then simply return a falsey value.
``` js
const ignorePrivate = format((info, opts) => {
if (info.private) { return false; }
return info;
});
console.dir(ignorePrivate.transform({
level: 'error',
message: 'Public error to share'
}));
// { level: 'error', message: 'Public error to share' }
console.dir(ignorePrivate.transform({
level: 'error',
private: true,
message: 'This is super secret - hide it.'
}));
// false
```
Use of `format.combine` will respect any falsey values return and stop evaluation of later formats in the series. For example:
``` js
const { format } = require('logform');
const { combine, timestamp, label } = format;
const willNeverThrow = format.combine(
format(info => { return false })(), // Ignores everything
format(info => { throw new Error('Never reached') })()
);
console.dir(willNeverThrow.transform({
level: 'info',
message: 'wow such testing'
}))
```
## Formats
### Align
The `align` format adds a `\t` delimiter before the message to align it in the same place.
```js
const { format } = require('logform');
const alignFormat = format.align();
const info = alignFormat.transform({
level: 'info',
message: 'my message'
});
console.log(info);
// { level: 'info', message: '\tmy message' }
```
This was previously exposed as `{ align: true }` in `winston < 3.0.0`.
### CLI
The `cli` format is a combination of the `colorize` and the `padLevels` formats. It turns a log `info` object into the same format previously available in `winston.cli()` in `winston < 3.0.0`.
```js
const { format } = require('logform');
const LEVEL = Symbol.for('level');
const cliFormat = format.cli({ colors: { info: 'blue' }});
const info = cliFormat.transform({
[LEVEL]: 'info',
level: 'info',
message: 'my message'
}, { all: true });
console.log(info);
// { level: '\u001b[34minfo\u001b[39m',
// message: '\u001b[34m my message\u001b[39m',
// [Symbol(level)]: 'info',
// [Symbol(message)]:
// '\u001b[34minfo\u001b[39m:\u001b[34m my message\u001b[39m' }
```
### Colorize
The `colorize` format adds different colors depending on the log level to the message and/or level.
It accepts the following options:
* **level**: If set to `true` the color will be applied to the `level`.
* **all**: If set to `true` the color will be applied to the `message` and `level`.
* **message**: If set to `true` the color will be applied to the `message`.
* **colors**: An object containing the colors for the log levels. For example: `{ info: 'blue', error: 'red' }`
```js
const { format } = require('logform');
const LEVEL = Symbol.for('level');
const colorizeFormat = format.colorize({ colors: { info: 'blue' }});
const info = colorizeFormat.transform({
[LEVEL]: 'info',
level: 'info',
message: 'my message'
}, { all: true });
console.log(info);
// { level: '\u001b[34minfo\u001b[39m',
// message: '\u001b[34mmy message\u001b[39m',
// [Symbol(level)]: 'info' }
```
This was previously exposed as `{ colorize: true }` to transports in `winston < 3.0.0`.
### Combine
The `combine` Format allows to combine multiple formats:
```js
const { format } = require('logform');
const { combine, timestamp, json } = format;
const jsonWithTimestamp = combine(
timestamp(),
json()
);
const info = jsonWithTimestamp.transform({
level: 'info',
message: 'my message'
});
console.log(info);
// { level: 'info',
// message: 'my message',
// timestamp: '2018-10-02T15:03:14.230Z',
// [Symbol(message)]:
// '{"level":"info","message":"my message","timestamp":"2018-10-02T15:03:14.230Z"}' }
```
### Errors
The `errors` format allows you to pass in an instance of a JavaScript `Error`
directly to the logger. It allows you to specify whether not to include the
stack-trace.
```js
const { format } = require('logform');
const { errors } = format;
const errorsFormat = errors({ stack: true })
const info = errorsFormat.transform(new Error('Oh no!'));
console.log(info);
// Error: Oh no!
// at repl:1:13
// at ContextifyScript.Script.runInThisContext (vm.js:50:33)
// at REPLServer.defaultEval (repl.js:240:29)
// at bound (domain.js:301:14)
// at REPLServer.runBound [as eval] (domain.js:314:12)
// at REPLServer.onLine (repl.js:468:10)
// at emitOne (events.js:121:20)
// at REPLServer.emit (events.js:211:7)
// at REPLServer.Interface._onLine (readline.js:282:10)
// at REPLServer.Interface._line (readline.js:631:8)
```
It will also handle `{ message }` properties as `Error` instances:
```js
const { format } = require('logform');
const { errors } = format;
const errorsFormat = errors({ stack: true })
const info = errorsFormat.transform({
message: new Error('Oh no!')
});
console.log(info);
// Error: Oh no!
// at repl:1:13
// at ContextifyScript.Script.runInThisContext (vm.js:50:33)
// at REPLServer.defaultEval (repl.js:240:29)
// at bound (domain.js:301:14)
// at REPLServer.runBound [as eval] (domain.js:314:12)
// at REPLServer.onLine (repl.js:468:10)
// at emitOne (events.js:121:20)
// at REPLServer.emit (events.js:211:7)
// at REPLServer.Interface._onLine (readline.js:282:10)
// at REPLServer.Interface._line (readline.js:631:8)
```
### JSON
The `json` format uses `safe-stable-stringify` to finalize the message.
It accepts the following options:
* **replacer**: A function that influences how the `info` is stringified.
* **space**: The number of white space used to format the json.
```js
const { format } = require('logform');
const jsonFormat = format.json();
const info = jsonFormat.transform({
level: 'info',
message: 'my message',
});
console.log(info);
// { level: 'info',
// message: 'my message',
// [Symbol(message)]: '{"level":"info","message":"my message"}' }
```
This was previously exposed as `{ json: true }` to transports in `winston < 3.0.0`.
### Label
The `label` format adds the specified `label` before the message or adds it to the `info` object.
It accepts the following options:
* **label**: A label to be added before the message.
* **message**: If set to `true` the `label` will be added to `info.message`. If set to `false` the `label` will be added as `info.label`.
```js
const { format } = require('logform');
const labelFormat = format.label();
const info = labelFormat.transform({
level: 'info',
message: 'my message'
}, { label: 'my label', message: true });
console.log(info);
// { level: 'info', message: '[my label] my message' }
```
This was previously exposed as `{ label: 'my label' }` to transports in `winston < 3.0.0`.
### Logstash
The `logstash` Format turns a log `info` object into pure JSON with the appropriate logstash options.
```js
const { format } = require('logform');
const { logstash, combine, timestamp } = format;
const logstashFormat = combine(
timestamp(),
logstash()
);
const info = logstashFormat.transform({
level: 'info',
message: 'my message'
});
console.log(info);
// { level: 'info',
// [Symbol(message)]:
// '{"@message":"my message","@timestamp":"2018-10-02T11:04:52.915Z","@fields":{"level":"info"}}' }
```
This was previously exposed as `{ logstash: true }` to transports in `winston < 3.0.0`.
### Metadata
The `metadata` format adds a metadata object to collect extraneous data, similar to the metadata object in winston 2.x.
It accepts the following options:
* **key**: The name of the key used for the metadata object. Defaults to `metadata`.
* **fillExcept**: An array of keys that should not be added to the metadata object.
* **fillWith**: An array of keys that will be added to the metadata object.
```js
const { format } = require('logform');
const metadataFormat = format.metadata();
const info = metadataFormat.transform({
level: 'info',
message: 'my message',
meta: 42
});
console.log(info);
// { level: 'info', message: 'my message', metadata: { meta: 42 } }
```
### PadLevels
The `padLevels` format pads levels to be the same length.
```js
const { format } = require('logform');
const LEVEL = Symbol.for('level');
const padLevelsFormat = format.padLevels();
const info = padLevelsFormat.transform({
[LEVEL]: 'info',
message: 'my message'
});
console.log(info);
// { message: ' my message', [Symbol(level)]: 'info' }
```
This was previously exposed as `{ padLevels: true }` to transports in `winston < 3.0.0`.
### PrettyPrint
The `prettyPrint` format finalizes the message using `util.inspect`.
It accepts the following options:
* **depth**: A `number` that specifies the maximum depth of the `info` object being stringified by `util.inspect`. Defaults to `2`.
* **colorize**: Colorizes the message if set to `true`. Defaults to `false`.
The `prettyPrint` format should not be used in production because it may impact performance negatively and block the event loop.
> **NOTE:** the `LEVEL`, `MESSAGE`, and `SPLAT` symbols are stripped from the
> output message _by design._
This was previously exposed as `{ prettyPrint: true }` to transports in `winston < 3.0.0`.
```js
const { format } = require('logform');
const prettyPrintFormat = format.prettyPrint();
const info = prettyPrintFormat.transform({
[LEVEL]: 'info',
level: 'info',
message: 'my message'
});
console.log(info);
// { level: 'info',
// message: 'my message',
// [Symbol(level)]: 'info',
// [Symbol(message)]: '{ level: \'info\', message: \'my message\' }' }
```
### Printf
The `printf` format allows to create a custom logging format:
```js
const { format } = require('logform');
const myFormat = format.printf((info) => {
return `${info.level} ${info.message}`;
})
const info = myFormat.transform({
level: 'info',
message: 'my message'
});
console.log(info);
// { level: 'info',
// message: 'my message',
// [Symbol(message)]: 'info my message' }
```
### Simple
The `simple` format finalizes the `info` object using the format: `level: message stringifiedRest`.
```js
const { format } = require('logform');
const MESSAGE = Symbol.for('message');
const simpleFormat = format.simple();
const info = simpleFormat.transform({
level: 'info',
message: 'my message',
number: 123
});
console.log(info[MESSAGE]);
// info: my message {number:123}
```
### Splat
The `splat` format transforms the message by using `util.format` to complete any `info.message` provided it has string interpolation tokens.
```js
const { format } = require('logform');
const splatFormat = format.splat();
const info = splatFormat.transform({
level: 'info',
message: 'my message %s',
splat: ['test']
});
console.log(info);
// { level: 'info', message: 'my message test', splat: [ 'test' ] }
```
Any additional splat parameters beyond those needed for the `%` tokens
(aka "metas") are assumed to be objects. Their enumerable properties are
merged into the `info`.
```js
const { format } = require('logform');
const splatFormat = format.splat();
const info = splatFormat.transform({
level: 'info',
message: 'my message %s',
splat: ['test', { thisIsMeta: true }]
});
console.log(info);
// { level: 'info',
// message: 'my message test',
// thisIsMeta: true,
// splat: [ 'test' ] }
```
This was previously exposed implicitly in `winston < 3.0.0`.
### Timestamp
The `timestamp` format adds a timestamp to the info.
It accepts the following options:
* **format**: Either the format as a string accepted by the [fecha](https://github.com/taylorhakes/fecha) module or a function that returns a formatted date. If no format is provided `new Date().toISOString()` will be used.
* **alias**: The name of an alias for the timestamp property, that will be added to the `info` object.
```js
const { format } = require('logform');
const timestampFormat = format.timestamp();
const info = timestampFormat.transform({
level: 'info',
message: 'my message'
});
console.log(info);
// { level: 'info',
// message: 'my message',
// timestamp: '2018-10-02T11:47:02.682Z' }
```
It was previously available in `winston < 3.0.0` as `{ timestamp: true }` and `{ timestamp: function:String }`.
### Uncolorize
The `uncolorize` format strips colors from `info` objects.
It accepts the following options:
* **level**: Disables the uncolorize format for `info.level` if set to `false`.
* **message**: Disables the uncolorize format for `info.message` if set to `false`.
* **raw**: Disables the uncolorize format for `info[MESSAGE]` if set to `false`.
This was previously exposed as `{ stripColors: true }` to transports in `winston < 3.0.0`.
## Tests
Tests are written with `mocha`, `assume`, and `nyc`. They can be run with `npm`:
```
npm test
```
##### LICENSE: MIT
##### AUTHOR: [Charlie Robbins](https://github.com/indexzero)
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