4.9 KiB
Logger
Environment-agnostic, ESM-friendly logger for simple needs.
Why does this exist?
I've been using debug for quite some time but wanted to migrate my projects to better ESM support. Alas, debug doesn't ship as ESM so I went and wrote this little logger just for my needs. You will likely see it printing useful data in Mock Service Worker and beyond.
Installation
npm install @open-draft/logger
Usage
This package has the same API for both browser and Node.js and can run in those environments out of the box.
// app.js
import { Logger } from '@open-draft/logger'
const logger = new Logger('parser')
logger.info('starting parsing...')
logger.warning('found legacy document format')
logger.success('parsed 120 documents!')
Logging is disabled by default. To enable logging, provide the DEBUG environment variable:
DEBUG=1 node ./app.js
You can also use
trueinstead of1. You can also use a specific logger's name to enable logger filtering.
API
- Class:
Logger
new Logger(name)
namestringthe name of the logger.
Creates a new instance of the logger. Each message printed by the logger will be prefixed with the given name. You can have multiple loggers with different names for different areas of your system.
const logger = new Logger('parser')
You can nest loggers via
logger.extend().
logger.debug(message, ...positionals)
messagestringpositionalsunknown[]
Prints a debug message.
logger.debug('no duplicates found, skipping...')
12:34:56:789 [parser] no duplicates found, skipping...
logger.info(message, ...positionals)
messagestringpositionalsunknown[]
Prints an info message.
logger.info('new parse request')
12:34:56:789 [parser] new parse request
logger.success(message, ...positionals)
messagestringpositionalsunknown[]
Prints a success message.
logger.success('prased 123 documents!')
12:34:56:789 ✔ [parser] prased 123 documents!
logger.warning(message, ...positionals)
messagestringpositionalsunknown[]
Prints a warning. In Node.js, prints it to process.stderr.
logger.warning('found legacy document format')
12:34:56:789 ⚠ [parser] found legacy document format
logger.error(message, ...positionals)
messagestringpositionalsunknown[]
Prints an error. In Node.js, prints it to process.stderr.
logger.error('failed to parse document')
12:34:56:789 ✖ [parser] failed to parse document
logger.extend(prefix)
prefixstringAdditional prefix to append to the logger's name.
Creates a new logger out of the current one.
const logger = new Logger('parser')
function parseRequest(request) {
const requestLogger = logger.extend(`${request.method} ${request.url}`)
requestLogger.info('start parsing...')
}
12:34:56:789 [parser] [GET https://example.com] start parsing...
logger.only(callback)
Executes a given callback only when the logging is activated. Useful for computing additional information for logs.
logger.only(() => {
const documentSize = getSizeBytes(document)
logger.debug(`document size: ${documentSize}`)
})
You can nest
logger.*methods in the callback tologger.only().
Log levels
You can specify the log levels to print using the LOG_LEVEL environment variable.
There are the following log levels:
debuginfosuccesswarningerror
Providing no log level will print all the messages.
Here's an example of how to print only warnings:
// app.js
import { Logger } from '@open-draft/logger'
const logger = new Logger('parser')
logger.info('some info')
logger.warning('some warning')
logger.error('some error')
LOG_LEVEL=warning node ./app.js
12:34:56:789 ⚠ [parser] some warning
Logger filtering
You can only print a specific logger by providing its name as the DEBUG environment variable.
// app.js
import { Logger } from '@open-draft/logger'
const appLogger = new Logger('app')
const parserLogger = new Logger('parser')
appLogger.info('starting app...')
parserLogger.info('creating a new parser...')
DEBUG=app node ./app.js
12:34:56:789 [app] starting app...