snog

A simple strutured logging library for node. Heavily inspired by Logrus.

npm i @openfin/snog

Latest Stable: 2.0.0

Usage

You can use snog directly aka the default global logger.

``javascript
import log from "@openfin/snog";
log.debug("hello");
`

Or clone / create a new one

`javascript
import log, { Snog } from "@openfin/snog";
const clonedLogger = log.clone();
const newLogger = new Snog();
`

See snog.clone for the difference between clone and new.

You can log with fields

`javascript
import log from "@openfin/snog";
log
.addField("I love", "pizza")
.addField("I love", "grits")
.addFields({ like: "oranges" })
.info("food i love");
// Note: Fields with the same name will override previous fields
`

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Logs the given values at the respective level

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Logs the given values after formatting with util.format. See documentation on util.format for more information.

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Adds a field to be logged when a logging method is called. Fields can over write each other, the latest one taking precendence. Also nothing is logged until a log method(eg log.info) is called

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Similar to .addField but takes an object instead of a key/value pair

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Set the log level using either the logLevel enum integer or a log level string(silly, debug, info, warn, error). If you pass something invalid it will not change the level. It will print a error message. Returns false if the level was not changed otherwise true.

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Takes the same options as creating a new Snog instance directly, only difference is that clone will merge defaultFields and keep custom formater, writer and previous level. Just a small convience function for those who want "child logger" like functionality.

Configuration

Both .clone and new Snog take the same options object.

* colorize OPTIONAL: Colorize the terminal output. If the environment variable NODE_ENV is set to production colorize is set to false, otherwise it defaults to true.
* defaultFields OPTIONAL: Fields to always log.
* level OPTIONAL: Log level. If the environment variable NODE_DEBUG is set to a valid level(see Log Levels), it will use that otherwise defaults to INFO
* date OPTIONAL: A function that returns a date object. This is used for testing and should never be set.
* writer OPTIONAL: The log writer, defaults to console.log.
* formatter OPTIONAL: The log formatter. Defaults to built in text formatter. See formatter section for more details

Format and Formatters

You can customize the output of Snog by using a custom formatter. Snog comes with two formatters, textFormatter and jsonFormatter. Snog defaults to textFormatter.

Text formatter output

2018-04-28T04:00:00.000Z INFO msg=Single added field I have='a field'

JSON formatter output

{"I have":"a field","msg":"Overriden","timestamp":"2018-04-28T04:00:00.000Z","level":"INFO","Field 1":1,"Field 2":"another field","im":"an object fields\\n","snog":"true","thisGetsOverriden":"YES"}

You can create your own formatter and pass it to snog provided it matches the formatter interface. For example here is the jsonFormatter

`typescript
//Snog fields contain the log message(msg), timestamp and level
// fields is the fields the caller added to the log using .addField and/or .addFields
export interface Formatter {
(snog: Snog, snogFields: SnogFields, fields: Map): any;
}

export function jsonFormatter(
snog: Snog,
snogFields: SnogFields,
fields: Map
) {
const k = Object.assign(snog.defaultFields, mapToObject(fields), snogFields, {
timestamp: snogFields.timestamp.toISOString(),
level: levelText[snogFields.level]
});
return JSON.stringify(k, null, 0) + "\n";
}
`

Writers

You can change where snog writes to by passing in a custom writer. The writer must be a function that takes a single value and can return anything(prefer void). By default snog uses console.log

Example custom writer

`typescript
function myAwesomeWriter(input) {
myCustomStream.write(input);
}
const logger = new Snog({ writer: myAwesomeWriter });
``

License

Apache 2.0 See LICENSE for more details