JsLog

JsLog (pronounced /ˈdʒəslɒɡ/), from "Just Log", is a simple, lightweight, and pluggable logger for JavaScript and TypeScript.

Features

• Simple and lightweight: No dependencies and a small footprint.
• Pluggable: Extend the logger's functionality with plugins.
• Multiple log levels: Supports trace, debug, info, log, warn, and error.
• TypeScript support: Written in TypeScript and includes type definitions.

Installation

npm install @geezgus/jslog

Usage

import { logger } from 'jslog';

logger.info('Hello, world!');
// Output: Hello, world!

logger.error('This is an error message.');
// Output: This is an error message.

With Plugins

JsLog's functionality can be extended with plugins. Here's an example of how to use the timestamp and levelFilter plugins:

import { logger as baseLogger } from 'jslog';
import { levelFilter, LogLevel, timestamp } from 'jslog/plugins';

const logger = baseLogger
  .use(timestamp('utc'))
  .use(levelFilter(LogLevel.Info));

logger.info('This message has a timestamp.');
// Output: [Thu, 03 Jul 2025 12:00:00 GMT] This message has a timestamp.

logger.debug('This message will be filtered out.');
// Output:

Plugins

JsLog's core is small and simple. All additional features are implemented as plugins.

Included Plugins

• levelFilter: Filters log messages based on their severity level.
• timestamp: Adds a timestamp to the beginning of the log message.

Creating a Plugin

A plugin is just a function that receives the logger's context as an argument. The context contains the log method (e.g., info, error) and the arguments passed to it.

Here's an example of a plugin that adds a prefix to all log messages:

import { LoggerContext } from 'jslog';

const prefix = (text: string) => (ctx: LoggerContext) => {
  ctx.args.unshift(text);
};

const logger = baseLogger.use(prefix('[API]'));

logger.info('This is a message from the API.');
// Output: [API] This is a message from the API.

Development

Scripts

• npm run build: Builds the project.
• npm run dev: Runs the project in development mode.
• npm run lint: Lints the source code.
• npm run format: Formats the source code.

License

This project is licensed under the MIT License.