Crowlog - Extendable JS logging library

Crowlog is a simple, lightweight, zero-dependency, and extendable logging library for any JavaScript environment.

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Features

- Ultra lightweight - Crowlog is very lightweight (less than 1kB minified + gzipped, see comparison).
- Zero dependencies - No runtime dependencies, just pure JavaScript.
- Extendable - Crowlog is designed to be extendable, so you can add your own transports and plugins to it.
- Simple - Crowlog is designed to be simple and easy to use.
- Fully typed - Crowlog is fully typed, so you can get autocomplete and type safety when using it.
- Any environment - Crowlog works in any environment, including Node.js, browsers, and the edge.
- Testing friendly - Crowlog is designed to be testing friendly, so you can easily test your logs with the in-memory transport.
- Slightly opinionated - Crowlog is designed to be slightly opinionated, so it has a default transport and some plugins.
- Pretty logs - Crowlog pretty log command to display logs in a more readable format for development.

Installation

``bash


pnpm

pnpm install @crowlog/logger

npm

npm install @crowlog/logger

yarn

yarn add @crowlog/logger
`

Usage

Basic usage:

`typescript
import { createLogger } from '@crowlog/logger';

const logger = createLogger({ namespace: 'my-app' });

logger.info('Hello world');
logger.error({ error: new Error('...') }, 'Something went wrong');
`

> [!NOTE]
> The logging interface is either a single string message or a data object and a message string tuple.
> `typescript
> logger.info('Hello world');
> logger.info({ foo: 'bar' }, 'Hello world');
> `

$3

Crowlog logger provides 4 different logging methods: debug, info, warn, and error.

`typescript
logger.debug(/ ... /);
logger.info(/ ... /);
logger.warn(/ ... /);
logger.error(/ ... /);
`

$3

Crowlog logger provides a createChildLogger method to create a child logger that inherit the configuration of the parent logger.

`typescript
import { createLogger } from '@crowlog/logger';

const logger = createLogger({ namespace: 'my-app' });
const childLogger = logger.createChildLogger({ namespace: 'child' });
`

Alternatively, you can use the createLoggerFactory to create a logger factory that can be used to create child loggers with the same configuration.

`typescript
import { createLoggerFactory } from '@crowlog/logger';

const createLogger = createLoggerFactory({ transports: / ... /, plugins: / ... / });
const logger = createLogger({ namespace: 'child' });
`

Transports

Transports control where logs are sent. By default, Crowlog uses the stdout transport (outputs JSON to console).

`typescript
import { createLogger, createStdoutLoggerTransport } from '@crowlog/logger';

// Customize serialization
const logger = createLogger({
namespace: 'my-app',
transports: [
createStdoutLoggerTransport({
serialize: ({ level, message }) => [${level}] ${message}
})
]
});
`

For testing, use the in-memory transport:

`typescript
import { createInMemoryLoggerTransport } from '@crowlog/logger';

const inMemoryTransport = createInMemoryLoggerTransport();
const logger = createLogger({
namespace: 'my-app',
transports: [inMemoryTransport]
});

logger.info('Test log');
const logs = inMemoryTransport.getLogs({ excludeTimestampMs: true });
`

See the full documentation for more details on transports and how to create custom ones.

Plugins

Plugins extend logger functionality with filtering, redaction, and context management.

$3

Control which logs reach transports:

`typescript
import { createLogger, createFilterPlugin } from '@crowlog/logger';

const logger = createLogger({
namespace: 'my-app',
plugins: [
createFilterPlugin({
minLevel: 'info', // Only info and above
excludedNamespaces: ['debug-utils'] // Exclude specific namespaces
})
]
});
`

$3

Automatically hide sensitive data:

`typescript
import { createRedactPlugin } from '@crowlog/logger';

const logger = createLogger({
namespace: 'my-app',
plugins: [
createRedactPlugin({
paths: ['password', 'apiKey', 'user.email']
})
]
});

logger.info({ password: 'secret', username: 'alice' }, 'Login');
// Output: { password: '[redacted]', username: 'alice' }
`

$3

Add application-wide context to all logs:

`typescript
import { createGlobalLogContextPlugin } from '@crowlog/logger';

const { globalContextPlugin, setGlobalLogContext } = createGlobalLogContextPlugin();

const logger = createLogger({
namespace: 'my-app',
plugins: [globalContextPlugin]
});

setGlobalLogContext({ environment: 'production', version: '1.0.0' });
logger.info('Started'); // Includes environment and version
`

$3

Add request-scoped context (requires async_hooks support):

`typescript
import { createAsyncContextPlugin, wrapWithLoggerContext } from '@crowlog/async-context-plugin';

const logger = createLogger({
namespace: 'my-app',
plugins: [createAsyncContextPlugin()]
});

wrapWithLoggerContext({ requestId: '123' }, () => {
logger.info('Processing'); // Includes requestId
});
`

See the full documentation for more details on plugins and how to create custom ones.

Pretty Logging

Format JSON logs for development with @crowlog/pretty:

`bash
node index.js | npx crowlog-pretty
`

!log-screenshot

See the pretty logging guide for more details.

Testing

Use the in-memory transport to capture logs in tests, or the noop logger to disable logging entirely:

`typescript
import { createNoopLogger } from '@crowlog/logger';

// No logs will be produced
const result = doSomething({ logger: createNoopLogger() });
``

See the testing guide for more details.

Comparison

| Library | Runtime dependencies | Bundled size |
|---------|--------------|--------------|
| @crowlog/logger@1.0.0 | 0 dependencies | 1.3kB (674B minified + gzipped) source |
| pino@9.6.0 | 11 dependencies | 7.5kB (2.9kb minified + gzipped) source |
| winston@3.17.0 | 11 dependencies | 147.9kB (37.4kB minified + gzipped) source |
| bunyan@1.8.15 | 19 dependencies | 15.7kB (5.6kB minified + gzipped) source |

License

This project is licensed under the MIT License. See the LICENSE file for more information.

Credits

This project is crafted with ❤️ by Corentin Thomasset.
If you find this project helpful, please consider supporting my work.

The icon is the Raven Rounded from the Material Symbols.