mnr-logger

Opinionated logger for Node.js

You may not need it!

This is a highly opinionated solution aimed at code reuse for a few private projects. You'd be better off using something popular, like winston and friends.

v3 Breaking Changes

• From v3, mnr-logger is an ESM-only module - you are not able to import it with require().

• Bump minimum supported version of Node.js to v20.

• Change type of meta parameter from any to unknown.

Archive documentation:

• v1;
• v2;

Installation

$ npm install --save mnr-logger

Usage example

import mnrLogger from 'mnr-logger';

const logger = mnrLogger({
  appName: 'my-cool-app',
  deploymentEnv: 'production'
});

const ERR = new Error('something went wrong');

logger.error(ERR, { transactionId: '12345' });
logger.warn(ERR, { transactionId: '12345' });
logger.info('take a look at foo stuff', { transactionId: '12345' });

What It Does

mnr-logger sends log messages to stderr (for error method), or stdout (for warn and info methods).

When process.env.NODE_ENV !== 'production', mnr-logger logs directly to stdout/stderr without any care how many lines it occupies. This is for development mode.

When process.env.NODE_ENV === 'production', mnr-logger creates a POJO with all the pieces of information it has received, then JSON.stringifies it, and sends to stdout/stderr a single line of text. This allows to treat every single line in your logs storage as one logging item and automate processing. After JSON.parsing this string, you'll get a POJO of the following form:

• {ISO Date string} timestamp - Timestamp of the moment mnr-logger received the message.

• {String} appName - Application name that mnr-logger was initialized with.

• {String} deploymentEnv - Application deployment environment label that mnr-logger was initialized with.

• {String} level - "error" for error() method; "warn" for warn() method; "info" for info() method.

• {String} error - JSON.stringified Error object that was sent to error() or warn() methods. You can JSON.parse it further to get a pretty formatted representation of the error.

• {Any} meta - Optional. Additional information that was sent to the logger.

• {String} message - Message passed to info() method.

API Reference

mnrLogger(opts: object)

Create a logger instance. You can create as many logger instances as you need in your app.

• {String} opts.appName - [optional] Application name tag. Defaults to an empty string

• {String} deploymentEnv - [optional] Application deployment environment tag. Defaults to an empty string

Returns logger instance with error, warn, and info methods.

logger.error(error, [meta])

Logs an error (with some meta data) into stderr.

Parameters:

• {Error} error - Error to log

• {Any} [meta] - [optional] Any JSON-serializable data.

logger.warn(error, [meta])

Logs an error (with some meta data) into stdout.

Parameters:

• {Error} error - Error to log

• {Any} [meta] - [optional] Any JSON-serializable data.

logger.info(message, [meta])

Logs an arbitrary text message (with some meta data) into stdout.

Parameters:

• {String} message

• {Any} [meta] - [optional] Any JSON-serializable data.