@thi.ng/logger

[!NOTE] This is one of 201 standalone projects, maintained as part of the @thi.ng/umbrella monorepo and anti-framework.

🚀 Please help me to work full-time on these projects by sponsoring me on GitHub. Thank you! ❤️

• About
  • Log levels
  • Logging hierarchies
  • Supplied implementations
  • Lazy evaluation
• Status
• Related packages
• Installation
• Dependencies
• Usage examples
• API
• Authors
• License

About

Basis types for arbitrary & hierarchical logging.

The types & implementations provided by this package are used in various places throughout the thi.ng/umbrella ecosystem and can be swapped out on demand to customize users' needs.

Log levels

All loggers based on this basic framework provided by this package support the following LogLevels (in order of importance):

• FINE
• DEBUG
• INFO
• WARN
• SEVERE

Logging calls targeting lower levels than configured in the logger will be ignored.

Logging hierarchies

Each ILogger instance (i.e. all supplied here) can have an associated parent logger to which any non-filtered messages can be propagated. This allows for the easy creation of logging hierarchies with each logger able to control its own log level.

To that end the package also provides a ROOT logger.

import { ConsoleLogger, ROOT } from "@thi.ng/logger";

// create a child logger
const myLogger = ROOT.childLogger("custom");

// use console output for root logger (and for all its children)
ROOT.set(new ConsoleLogger());

// forwards message to root and then writes to console
myLogger.debug("hello");

// [DEBUG] custom: hello

Supplied implementations

The following logger implementations are provided:

• ConsoleLogger: writes output to console
• MemoryLogger: writes output to in-memory journal
• ProxyLogger: proxy impl for another logger
• StreamLogger: writes output to NodeJS stream
• NULL_LOGGER: no-op logger, suppresses all output

Lazy evaluation

Log messages can contain any number & types of arguments. No-arg functions can be provided as message arg to avoid evaluation of potentially costly message formatting for suppressed log levels. For example:

import { ConsoleLogger, LogLevel } from "@thi.ng/logger";

const logger = new ConsoleLogger("app", LogLevel.INFO);

const name = "thi.ng";

// eager (standard) arg evaluation
logger.info(`hello, ${name}`);
// [INFO] app: hello, thi.ng

// eager (standard) arg evaluation, but suppressed output
logger.debug("result is", 23 + 42);

// lazy arg evaluation
logger.info("result is", () => 23 + 42);
// [INFO] app: result is 65

Status

STABLE - used in production

Search or submit any issues for this package

Related packages

• @thi.ng/rstream-log - Structured, multilevel & hierarchical loggers based on @thi.ng/rstream

Installation

yarn add @thi.ng/logger

ESM import:

import * as log from "@thi.ng/logger";

Browser ESM import:

<script type="module" src="https://esm.run/@thi.ng/logger"></script>

JSDelivr documentation

For Node.js REPL:

const log = await import("@thi.ng/logger");

Package sizes (brotli'd, pre-treeshake): ESM: 871 bytes

Dependencies

None

Usage examples

One project in this repo's /examples directory is using this package:

Screenshot	Description	Live demo	Source
	Declarative component-based system with central rstream-based pubsub event bus	Demo	Source

API

Generated API docs

TODO

Authors

• Karsten Schmidt

If this project contributes to an academic publication, please cite it as:

@misc{thing-logger,
  title = "@thi.ng/logger",
  author = "Karsten Schmidt",
  note = "https://thi.ng/logger",
  year = 2016
}

License

© 2016 - 2025 Karsten Schmidt // Apache License 2.0