fn-logger-decorator

A lightweight TypeScript/JavaScript decorator to automatically log function errors and metadata to a file, console, or custom transport — ideal for observability and debugging in both development and production environments.

✨ Features

✅ Works with async/sync functions

🧠 Automatically logs:

Timestamp

Function name

Duration of execution

Error message

Stack trace (only in development)

Function arguments (optional)

🔐 Environment-aware (safe logs in production)

🧩 Pluggable transport: file, console, or custom

🛠️ Built with TypeScript, supports JavaScript (via Babel)

📦 Installation

npm install fn-logger-decorator

-- npm i node-ts to run this package

For TypeScript projects:

npm install reflect-metadata

Ensure experimentalDecorators and emitDecoratorMetadata are enabled in tsconfig.json.

🚀 Usage

1. Basic Usage

import 'reflect-metadata'; import { LogErrors } from 'fn-logger-decorator';

class DemoService { @LogErrors() async riskyOperation(input: string) { if (input === 'fail') throw new Error('Something went wrong'); return input.toUpperCase(); } }

2. Customize Options

@LogErrors({ logDir: 'custom-logs', // default is "logs" includeArgs: true, // include function args (default: true) transport: 'console', // 'file' | 'console' })

3. Custom Transport

@LogErrors({ customTransport: (entry) => { sendToMonitoringService(entry); // your logic here } })

📁 Output Example (file log)

Each log line is a JSON object:

{ "timestamp": "2025-07-10T09:45:23.123Z", "function": "riskyOperation", "durationMs": 12, "environment": "production", "args": ["fail"], "error": { "message": "Something went wrong" } }

🌐 Environment Support

Set NODE_ENV=production to strip stack traces.

Use cross-env for cross-platform scripts:

npx cross-env NODE_ENV=production ts-node yourfile.ts

✅ Requirements

Node.js v14+

TypeScript 4.0+

🧪 Testing

npm run test

🔒 Best Practices

Avoid logging PII in production

Use custom transport for sending logs to remote servers (e.g., Sentry, Datadog)

Wrap decorators around meaningful boundaries (e.g., API routes, service methods)

🧱 Future Roadmap

📃 License

MIT © 2025 Gowtham SSR

Feel free to contribute or submit feature requests on GitHub!