js-logger

This library provides a JavaScript/TypeScript logger inspired by Python's logger.

• Simple logging with default handlers supporting console.log, console.error, and process.stderr.
• Fast, logging level checks or log filters are applied before log records are created
• Complex log records properties support lazy evaluation, so they evaluated only when they need to be rendered
• Flexible composition of loggers, handlers and formatters
• Custom formatting using template literals
• Supports structured logging through a JSON formatter
• Supports hierarchical logging through parent-child logger graph
• CI/CD tests on Linux, MacOS and Windows
• Zero runtime dependencies!
• Comprehensive continuous benchmarks in CI/CD

Installation

npm install --save @matrixai/logger

Usage

import Logger, { LogLevel, StreamHandler, formatting } from '@matrixai/logger';

const logger = new Logger('root', LogLevel.INFO, [
  new StreamHandler(
    formatting.format`${formatting.date}:${formatting.level}:${formatting.key}:${formatting.msg}:${formatting.data}`,
  ),
]);

logger.debug('Hello world', { a: { b: [123, 456] } });
logger.info('Hello world', { 123: { b: [123, 456] } });
logger.warn('Hello world', { lazy: () => 'string' });
logger.error('Hello world', formatting.format`my custom format`);

const loggerChild = logger.getChild('child');

loggerChild.info(
  'Hello world',
  { 123: { b: [123, 456] } },
  formatting.format`${formatting.keys}:${formatting.msg}:${formatting.data}`,
);

There's lots more options available in the source code. See the docs and see the source code for more details.

Development

Run nix develop, and once you're inside, you can use:

# install (or reinstall packages from package.json)
npm install
# build the dist
npm run build
# run the repl (this allows you to import from ./src)
npm run tsx
# run the tests
npm run test
# lint the source code
npm run lint
# automatically fix the source
npm run lintfix

Docs Generation

npm run docs

See the docs at: https://matrixai.github.io/js-logger/

Publishing

Publishing is handled automatically by the staging pipeline.

Prerelease:

# npm login
npm version prepatch --preid alpha # premajor/preminor/prepatch
git push --follow-tags

Release:

# npm login
npm version patch # major/minor/patch
git push --follow-tags

Manually:

# npm login
npm version patch # major/minor/patch
npm run build
npm publish --access public
git push
git push --tags