@kocal/logger

logger

The Node.js logger I have always dreamed of.

Installation

$ yarn add @kocal/logger

Usage

Basic usage

import { Logger } from '@kocal/logger';
// or
const { Logger } = require('@kocal/logger');

// Default logger
const logger = Logger.getLogger();

logger.debug('My message');
// Write `2019-01-15T12:30:10.000Z:: default :: debug :: My message`
logger.log('My message');
// Write `2019-01-15T12:30:10.000Z :: default :: log :: My message`
logger.info('My message');
// Write `2019-01-15T12:30:10.000Z :: info :: My message`
logger.warn('My message');
// Write `2019-01-15T12:30:10.000Z :: default :: warn :: My message`
logger.error('My message');
// Write `2019-01-15T12:30:10.000Z :: default :: error :: My message`

// Named logger
const namedLogger = Logger.getLogger('my-name');

namedLogger.debug('My message');
// Write `2019-01-15T12:30:10.000Z :: my-name :: debug :: My message`

Custom level

Available levels are:

• error
• warn
• info (default)
• log
• debug

// at initialization
const logger = Logger.getLogger('my-logger', {
  level: 'info',
});

// at runtime
logger.level = 'info'; 
// or 
logger.setLevel('info');

// will display something
logger.error('Message'); 
logger.warn('Message');
logger.info('Message');

// won't display anything
logger.log('Message');
logger.debug('Message'); 

Custom format

The default format is: Date.toISOString() :: loggerName :: levelColor(level) :: message.

You can override the format at any moment by calling logger.setFormat():

const logger = Logger.getLogger();

logger.format = (context, variables) => {
  return `${context.date.toISOString()} :: ${context.message}`
}
// or
logger.setFormat((context, variables) => {
    return `${context.date.toISOString()} :: ${context.message}`
})

logger.log('My message');
// Write `2019-01-15T12:30:10.000Z :: My message`

Formatting the date

In version 2.0, Luxon dependency has been removed because its weight is about ~85kB, and ~77% of the size of the logger is due to Luxon.

To format the date, you can use date-fns format method:

import { Logger } from '@kocal/logger';
import { format as formatDate } from 'date-fns';

const logger = Logger.getLogger();
logger.format = (context, variables) => {
  return `${formatDate(context.date, 'YYYY-MM-DD HH:mm:ss')} :: ${context.message}`;
}

logger.log('My message');
// Write `2019-01-15 13:13:10 :: My message`

Variables

You can specify static or dynamic variables like that:

const logger = Logger.getLogger();

logger.format = (context, variables) => {
  return `${context.date} :: ${context.message} :: vars = ${JSON.stringify(variables)}`;
}

// pass a plain object
logger.variables = { count: 9000, foo: 'bar' }
// or a function that will be called at each time you log something
let anotherVariable = 'bar';
logger.variables = () => ({ count: 9000, foo: anotherVariable });

// or
logger.setVariables({ count: 9000, foo: 'bar' })
logger.setVariables(() => ({ count: 9000, foo: anotherVariable }))

logger.log('My message');
// Write `2019-01-15T12:30:10.000Z :: My message :: vars = {"count":9000,"foo":"bar"}`

Additional variables

All logs methods have a 2nd parameters where you can pass additional variables:

// pass a plain object
logger.log('My message', { count: 1234 });
// Write `2019-01-15T12:30:10.000Z :: My message :: vars = {"count":1234,"foo":"bar"}`

// or a function
logger.log('My message', () => ({ count: 1234 }));
// Write `2019-01-15T12:30:10.000Z :: My message :: vars = {"count":1234,"foo":"bar"}`

API

.getLogger( name = 'default', options = {}): Logger

Returns a singleton.

Parameters:

• name: A name, 'default' by default
• options:
  • options.format: check .setFormat
  • options.variables check setVariables

.setFormat( (context, variables) => '...' ): void

Customize log messages format.

Parameters:

• context:
  • context.name: logger's name, 'default' by default
  • context.level: 'debug', 'log', 'info', 'warn', or 'error'
  • context.levelColor: the color that represents level
  • context.message: your message
  • context.chalk: an instance of chalk
  • context.date: an instance of Date
• variables: a fusion of variables defined with .setVariables and additional variables from logging methods

.debug( message, additionalVariables = {} | Function ): void

.log( message, additionalVariables = {} | Function ): void

.info( message, additionalVariables = {} | Function ): void

.warn( message, additionalVariables = {} | Function ): void

.error( message, additionalVariables = {} | Function ): void

Log a message.

Parameters:

• message: your message 🤷🏻
• additionalVariables: variables that will be merged with logger's variables.