@verycrazydog/level-logger

A flexible logger supports log level. Inpired by console-log-level, got and loglevel.

level-logger was created because of inability to perform certain tasks on existing propular logging modules:

• Unable processing message parameters after logging level check to avoid unnecessary string processing.
• Not convenient to alter message prefix.
• ~~winston did not support multiple message parameters~~ it was supported via format.splat() but unfortunately unable to find out at the time of inventing level-logger.
• console-log-level hardcoded message level to logging function mapping.

The design of level-logger was inpired by:

• console-log-level, level-logger is designed to be simple to use.
• .extend() of got, .extend() method was added for conveniently alter the behavior of logger.
• methodFactory of loglevel, level-logger is highly customizable.

Install

npm install @verycrazydog/level-logger

Usage

Console logging

const { LevelLogger } = require('@verycrazydog/level-logger')
const logger = new LevelLogger({
	level: 'INFO'
})
// Print 'Hello World!'
logger.info('Hello World!')

Console logging with timestamp prefix

const { LevelLogger, LogTags } = require('@verycrazydog/level-logger')
const logger = new LevelLogger({
	level: 'INFO',
	prefixes: [ LogTags.TIMESTAMP ]
})
// Print '2020-10-13 20:02:11 Hello World!'
logger.info('Hello World!')

Custom timestamp format

const { LevelLogger, LogTags } = require('@verycrazydog/level-logger')
const logger = new LevelLogger({
	level: 'INFO',
	prefixes: [ LogTags.TIMESTAMP ],
	timestampFormatter: value => {
		const hour = value.getHours().toString().padStart(2, '0')
		const minute = value.getMinutes().toString().padStart(2, '0')
		const second = value.getSeconds().toString().padStart(2, '0')
		return `${hour}:${minute}:${second}`
	}
})
// Print '20:54:26 Hello World!'
logger.info('Hello World!')

Use .extend() to create per-request logger

const { LevelLogger, LogTags } = require('@verycrazydog/level-logger')
const express = require('express')

const logger = new LevelLogger({
	level: 'INFO',
	prefixes: [ LogTags.TIMESTAMP, 'SERVER' ]
})
const reqLoggerBase = logger.extend({
	prefixes: [ LogTags.TIMESTAMP, 'REQUEST' ]
})

const app = express()
const port = 3000

app.get('/', (req, res) => {
	const reqId = Math.round(Math.random() * 99999999).toString().padStart(8, '0')
	const reqLogger = reqLoggerBase.extend({
		prefixes: [
			...reqLoggerBase.prefixes,
			reqId
		]
	})
	// Print '2020-10-13 20:22:29 REQUEST 80419951 GET /'
	reqLogger.info(req.method, req.path)
	res.send('Hello World!')
})

app.listen(port, () => {
	// Print '2020-10-13 20:22:28 SERVER Server running at port 3000'
	logger.info('Server running at port', port)
})

Process message for AWS CloudWatch to display as single log entry with formatted JSON display

const { LevelLogger, LogTags, defaultMessageFormatter } = require('@verycrazydog/level-logger')
const logger = new LevelLogger({
	level: 'INFO',
	prefixes: [ LogTags.TIMESTAMP ],
	messageFormatter: (level, resolvedPrefixes, ...messageParams) => {
		messageParams = messageParams.map(p => {
			if (typeof p === 'object' && !(p instanceof Error)) {
				return JSON.stringify(p)
			} else {
				return p
			}
		})
		let message = defaultMessageFormatter(level, resolvedPrefixes, ...messageParams)
		// Reference https://stackoverflow.com/a/44272913/1131246
		message = message.replace(/\r?\n/g, '\r')
		return message
	}
})
logger.info({ message: 'Hello World!' })
logger.error(new Error('Test Error'))

Combine with other logger to log to file

const { LevelLogger, LogTags } = require('@verycrazydog/level-logger')
const winston = require('winston')

const winstonLogger = winston.createLogger({
	level: 'debug',
	format: winston.format.printf(({ message }) => {
		return message
	}),
	transports: [
		new winston.transports.Console(),
		new winston.transports.File({ filename: 'app.log' })
	]
})
const logger = new LevelLogger({
	level: 'DEBUG',
	prefixes: [ LogTags.TIMESTAMP, LogTags.MESSAGE_LEVEL ],
	logger: (level, message) => {
		winstonLogger.log(level, message)
	}
})

// Print '2020-10-13 20:51:07 INFO Hello World!' to both console and log file
logger.info('Hello World!')

License

This module is licensed under the MIT License.