etholog

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

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.

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.

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.

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	Send logs to Sentry for React Native
@etholog/async-storage-transport	Stores logs in asynchronous storage, such as AsyncStorage for React Native
@etholog/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.

import { createTransport } from "etholog";

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

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