@openreachtech/mentsu-logger

A thin logger wrapper around winston with daily log-file rotation.

Overview

mentsu-logger provides a small, uniform logging interface (log / warn / error / debug) on top of winston. It adds:

• printf-style message formatting (via util.format) through a params array.
• tag support, automatically appending the current process id as a pid:<pid> tag.
• output to both the console and daily-rotated log files (a general log and an error-only log).
• environment-gated output: log entries are written only when NODE_ENV is production.

All logging methods return the logger instance, so calls can be chained.

Installation

Requires Node.js 20.x (the version the CI builds against).

npm install @openreachtech/mentsu-logger

It is an ES module ("type": "module"); import it with ESM import syntax.

Usage

Create a logger with MentsuLogger.create(), then call one of the level methods.

import { MentsuLogger } from '@openreachtech/mentsu-logger'

const alphaLogger = MentsuLogger.create({
  filePath: 'logs/app-',
  env: {
    NODE_ENV: 'production',
  },
})

// Simple message.
alphaLogger.log({
  message: 'What a beautiful day',
})

// printf-style formatting via `params`.
alphaLogger.warn({
  message: 'I have %d apples',
  params: [3],
})

// Custom tags (a `pid:<pid>` tag is appended automatically).
alphaLogger.error({
  message: 'Job failed',
  tags: [
    'job:AlphaSummarizer',
  ],
})

// Methods return the instance, so calls can be chained.
alphaLogger
  .debug({ message: 'step 1' })
  .debug({ message: 'step 2' })

Log entries are written only when env.NODE_ENV is production. With any other value, the level methods return the instance without emitting anything, which keeps non-production environments quiet without changing call sites.

Each entry is sent to the console and to daily-rotated files derived from filePath: a general log (<filePath>%DATE%.log) and an error-only log (<filePath>%DATE%.error.log).

API

Class members are written with the following notation.

| notation | members | | :-- | :-- | | #instanceProperty | instance property | | #instanceMethod() | instance method | | #get:instanceGetter | instance getter | | #set:instanceSetter | instance setter | | .staticProperty | static property | | .staticMethod() | static method | | .get:staticGetter | static getter | | .set:staticSetter | static setter |

MentsuLogger

The logger class exported by this package.

.create()

Factory method. Creates a MentsuLogger backed by a winston logger client.

MentsuLogger.create({
  filePath,
  maxFileSize,
  env,
  nodeProcess,
})

| parameter | type | required | description | | :-- | :-- | :-- | :-- | | filePath | string | yes | Base path used to build the rotated log file names. | | maxFileSize | number | no | Maximum size (in bytes) of a rotated file. Defaults to 1048576 (1 MiB). | | env | { [key: string]: string } | no | Environment map. NODE_ENV gates whether entries are written (production enables output). | | nodeProcess | { pid: number } | no | Process-like object. Defaults to the global process; its pid is appended as a pid:<pid> tag. |

Returns a MentsuLogger instance.

#log()

Writes an entry at the info level.

alphaLogger.log({
  message,
  params,
  tags,
})

| parameter | type | required | description | | :-- | :-- | :-- | :-- | | message | string | yes | Message, optionally with util.format placeholders (e.g. %s, %d). | | params | Array<*> | no | Values substituted into the message placeholders. Defaults to []. | | tags | Array<string> | no | Tags attached to the entry. A pid:<pid> tag is appended automatically. Defaults to []. |

Returns the MentsuLogger instance for method chaining.

#warn()

Writes an entry at the warn level. Same parameters and return value as #log().

#error()

Writes an entry at the error level. Same parameters and return value as #log().

#debug()

Writes an entry at the debug level. Same parameters and return value as #log().

Contribution

Bug reports, feature requests, and code contributions are welcome.

Feel free to contact us through GitHub Issues.

git clone https://github.com/openreachtech/mentsu-logger.git
cd mentsu-logger
npm install
npm run lint
npm test

License

This project is released under the MIT License.

For more details, please see in the LICENSE file.

Developer

Open Reach Tech Inc.

Copyright

© 2026 Open Reach Tech Inc.