Basis types for arbitrary & hierarchical logging
npm install @thi.ng/logger
!npm downloads

> [!NOTE]
> This is one of 214 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
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.
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.
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.
``ts
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
`
The following logger implementations are provided:
- ConsoleLogger: writes output to consoleMemoryLogger
- : writes output to in-memory journalProxyLogger
- : proxy impl for another loggerStreamLogger
- : writes output to NodeJS streamNULL_LOGGER
- : no-op logger, suppresses all output
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:
`ts
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
`
STABLE - used in production
Search or submit any issues for this package
- @thi.ng/rstream-log - Structured, multilevel & hierarchical loggers based on @thi.ng/rstream
`bash`
yarn add @thi.ng/logger
ESM import:
`ts`
import * as log from "@thi.ng/logger";
Browser ESM import:
`html`
For Node.js REPL:
`js`
const log = await import("@thi.ng/logger");
Package sizes (brotli'd, pre-treeshake): ESM: 914 bytes
None
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 |
TODO
If this project contributes to an academic publication, please cite it as:
`bibtex``
@misc{thing-logger,
title = "@thi.ng/logger",
author = "Karsten Schmidt",
note = "https://thi.ng/logger",
year = 2016
}
© 2016 - 2026 Karsten Schmidt // Apache License 2.0