# etholog

> A universal customizable logger

Latest version **0.4.0** (published 2026-09-23) · MIT license · 0 weekly downloads

## Install

```sh
npm install etholog
pnpm add etholog
yarn add etholog
bun add etholog
```

## Health

**Score 75/100 (B)** — status: active.

Positive: has types; esm support; no vulnerabilities; has provenance; recently updated; high maintenance score; high quality score.

Warnings: low downloads; pre 1.0.

## Facts

| | |
|---|---|
| Version | 0.4.0 |
| Published | 2026-09-23 |
| First published | 2025-02-23 |
| Weekly downloads | 0 |
| License | MIT |
| TypeScript types | bundled |
| Module format | ESM + CommonJS |
| Dependencies | 0 |
| Unpacked size | 81.1 KB |
| Known vulnerabilities | 0 |
| Install scripts | no |
| Provenance | attested (GitHub Actions) |
| GitHub stars | 0 |
| Author | Koen Gommers |
| Maintainers | koengommers |
| Keywords | log, logs, logging, logger, node, react-native, browser, debug, json |

## Links

- npm: https://www.npmjs.com/package/etholog
- Repository: https://github.com/koengommers/etholog
- Homepage: https://github.com/koengommers/etholog#readme
- npm.io page: https://npm.io/package/etholog

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## Recent versions

- 0.4.0 (latest) — 2026-09-23
- 0.3.1 — 2026-02-24
- 0.3.0 — 2026-02-19
- 0.2.1 — 2025-03-21
- 0.2.0 — 2025-02-23
- 0.1.2 — 2025-02-23
- 0.1.1 — 2025-02-23
- 0.1.0 — 2025-02-23

## README

# Etholog

A simple logging library designed to be compatible with various JavaScript runtimes, such as Node.js, React Native and the browser.

Etholog is named after ethology, the study of animal behavior under natural conditions.

## Installation

```bash
npm install etholog
```

## Basic usage

Etholog works with "transports", these can be seen as destinations for the logs. It requires one transport at the minimum. You can use one of the built-in transports or create your own.

```typescript
import { createLogger } from "etholog";

const logger = createLogger({
  transports: [
    consoleTransport(),
  ],
});

logger.info("Hello world!");
```

## Levels

Etholog supports the following log levels:

- `error`
- `warn`
- `info`
- `debug`

## Processors

Processors transform a log before any transport sees it. A processor takes a log and returns a log, or `null` to drop it. They run in order, after the level filter.

```typescript
import { createLogger } from "etholog";

const logger = createLogger({
  processors: [
    (log) => ({
      ...log,
      data: { ...log.data, time: new Date(log.timestamp).toISOString() },
    }),
  ],
  transports: [consoleTransport()],
});
```

Return a new log rather than modifying the one you were given.

### Serializing errors

`JSON.stringify(new Error("boom"))` returns `{}`, so an error in a log's data reaches JSON transports empty. The `serializeErrors()` processor converts errors into `{ name, message, stack }`, following `cause` chains and copying custom properties such as `code`. Recommended if any of your transports serialize to JSON.

```typescript
import { createLogger, serializeErrors } from "etholog";

const logger = createLogger({
  processors: [serializeErrors()],
  transports: [syncStorageTransport({ storage })],
});

logger.error("Request failed", { error: new Error("Timeout") });
// data.error is { name: "Error", message: "Timeout", stack: "..." }
```

It serializes errors under any key, walking `data` one level deep: `data.error` and `data.context.error` are serialized, `data.a.b.error` is not.

## Transports

Etholog comes with one built-in transport, the `consoleTransport`. There are various additional transports available as separate packages.

| Package | Description |
| --- | --- |
| [`@etholog/sentry-react-native-transport`](packages/sentry-react-native-transport) | Send logs to Sentry for React Native |
| [`@etholog/async-storage-transport`](packages/async-storage-transport) | Stores logs in asynchronous storage, such as AsyncStorage for React Native |
| [`@etholog/sync-storage-transport`](packages/sync-storage-transport) | Stores logs in synchronous storage, such as localStorage |

### Creating a custom transport

You can create your own transport by using the `createTransport` function.

```typescript
import { createTransport } from "etholog";

const customTransport = createTransport((log) => {
  // Do something with the log
});

const logger = createLogger({
  transports: [customTransport],
});
```

---
_Source: https://npm.io/package/etholog · Machine-readable twin of the npm.io package page. Health data is recomputed on every publish._