Log4U - A Flexible Logging Library for Node.js

Log4U is a lightweight, production-grade and flexible logging library for Node.js, written in TypeScript. Designed to make logging effortless and customizable, it supports structured logs, custom formats, and daily log rotation.

Features

• 🌟 Easy-to-Use: Minimal setup to start logging in seconds.
• 🛠️ Highly Configurable: Define your logging levels, formats, and more.
• 🕒 Daily Log Rotation: Automatically creates a new log file for each day.
• 📄 Rich Log Details: Supports structured logs with optional parameters like payloads, status codes, and URLs.
• 🔍 Error Handling: Logs complete error stack traces for debugging.
• ⚡ TypeScript Support: Fully typed for seamless integration.

Installation

Install the package using npm or yarn:

npm install log4u
# or
yarn add log4u

Getting Started

Step 1: Import and Initialize

Start by importing the Logger class and configuring it with your service name.

import Logger from 'log4u';

const logger = new Logger({ serviceName: 'MyService' });

Step 2: Logging Your Data

You can log structured data with minimal effort:

logger.log({
  type: 'INFO', // Log level: INFO, DEBUG, ERROR
  message: 'This is an informational log.', // Required
});

logger.log({
  type: 'DEBUG',
  message: 'Logging with additional details.',
  payload: { id: 123, action: 'test' }, // Optional payload
  statusCode: 200,                      // Optional status code
  sourceURL: 'http://localhost:3000',   // Optional source URL
  targetURL: 'http://localhost:5173',   // Optional target URL
});

Step 3: Logging Errors

Log errors directly with stack traces for debugging:

try {
  throw new Error('Something went wrong!');
} catch (err) {
  logger.log({
    type: 'ERROR',
    message: err, // Pass the error object directly
    logId: 'ERR001',
  });
}

Advanced: Adding Middleware for Request Logging

Log incoming requests in an Express.js backend:

import { Request, Response, NextFunction } from 'express';
import Logger from 'log4u';

const logger = new Logger({ serviceName: 'MyBackendService' });

function logRequest(req: Request, res: Response, next: NextFunction) {
  const logData: any = {
    type: 'INFO',
    message: 'Incoming request',
    sourceURL: req.get('Origin') || req.get('Referer'),
    targetURL: req.originalUrl,
    payload: req.body,
  };

  res.on('finish', () => {
    logData.statusCode = res.statusCode;
    logger.log(logData);
  });

  next();
}

// Use the middleware in your app
app.use(logRequest);

Configuration Options

When initializing the logger, you can pass the following options:

| Option | Type | Default | Description | |----------------|----------|-------------|-------------------------------------------------| | serviceName | string | undefined | The name of your service (included in logs). | | logDirectory | string | ./logs | Directory where log files are stored. | | dateFormat | string | YYYY-MM-DD| Format for daily log file names. |

Log Data Structure

Here’s a breakdown of the log data you can provide (to be added more in future):

| Field | Required | Type | Description | |--------------|----------|-----------------|--------------------------------------------------| | type | Yes | string | Log level: INFO, DEBUG, or ERROR. | | message | Yes | string/Error| A short description or error object. | | logId | No | string | Unique identifier for the log. | | payload | No | object | Any additional data related to the log. | | statusCode | No | number | HTTP status code (e.g., 200, 404, 500). | | sourceURL | No | string | Source of the request or action (e.g., API endpoint). | | targetURL | No | string | Target URL for the action. |

Example Log Output

For a simple log:

INFO 2024-11-30T12:00:00Z MyService Testing log package

For a log with additional details:

DEBUG 2024-11-30T12:05:00Z MyService Logging with additional details {"id":123,"action":"test"} 200 http://localhost:3000 http://localhost:5173

For an error log:

ERROR 2024-11-30T12:10:00Z MyService ERR001 Something went wrong!
Error: Something went wrong!
    at Object.<anonymous> (/path/to/file.js:10:15)
    ...

Happy Logging! 🎉