Homework 3: Logger functionality

Task Definition

Update method log of the Logger according to the requirements:

• config should contain property log_level
• Default value is "info"
• Logging rules:
  • log_level = severe → log only severe
  • log_level = warn → log severe, warn
  • log_level = info (default) → log severe, warn, info
  • log_level = debug → log everything except trace
  • log_level = trace → log all messages

Testing is based on different contents of index.ts and checking console or file output.

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Description 📝

This project implements a custom Logger in TypeScript with support for multiple log levels, timestamped messages, and colored console output. The Logger extends Node.js EventEmitter, allowing you to attach multiple handlers for specific log levels or for all messages.

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Purpose 🎯

The purpose of this homework is to practice:

• Event-driven programming using Node.js EventEmitter
• Configurable log levels via config
• Formatted and colorized console output
• Strong typing with TypeScript enums
• Handler-based logging architecture

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Features

• ✅ Supports log levels: severe, warn, info, debug, trace via enum LogLevel
• ✅ Configurable log_level in config (default: info)
• ✅ Only messages matching or exceeding the configured log level are logged
• ✅ Each log entry includes ISO timestamp
• ✅ Color-coded console output with symbols:
  • 🔴 severe (red)
  • 🟠 warn (orange)
  • 🟡 info (yellow)
  • 🟢 debug (green)
  • 🔵 trace (blue)
• ✅ addHandlerLevel(level, handler) for level-specific handling (e.g., writing to files)
• ✅ addHandlerMessage(handler) for handling all messages

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How It Works 🔍

1. Initialization
   The Logger reads log_level from a config file or defaults to LogLevel.info.

2. Logging a message

   • The log() method checks if the message’s level meets the configured log level using shouldLog().
   • If allowed, it generates a timestamp and formats the message with colors and symbols.
   • Emits the message to:
     • Level-specific handlers (addHandlerLevel) as a formatted string.
     • Global message handlers (addHandlerMessage) as an object containing level, formattedMessage.

3. Handlers
   Users can attach multiple handlers:

   • addHandlerLevel(level, handler): reacts to a specific log level.
   • addHandlerMessage(handler): reacts to all logged messages.

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Output 📜

Example console output with colors and symbols:

[2025-08-20T16:30:00.000Z] 🔴 [SEVERE] CRITICAL ERROR
[2025-08-20T16:30:01.000Z] 🟠 [WARN] Low disk space
[2025-08-20T16:30:02.000Z] 🟡 [INFO] User logged in
[2025-08-20T16:30:03.000Z] 🟢 [DEBUG] Debugging x=42
[2025-08-20T16:30:04.000Z] 🔵 [TRACE] Entered function foo()

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Usage 📦

1. Install dependencies:

npm install

2. Run the project:

npm run dev

3. Example in index.ts:

import Logger, { LogLevel } from "./Logger.js";

const logger = new Logger();

// Global handler for all messages
logger.addHandlerMessage((obj) => console.log(obj.formattedMessage));

// Level-specific handler
logger.addHandlerLevel(LogLevel.debug, (msg) =>
	fs.writeFileSync("logs.txt", "\n" + msg, { flag: "a" })
);

// Logging examples
logger.log(LogLevel.severe, "CRITICAL ERROR");
logger.log(LogLevel.warn, "Low disk space");
logger.log(LogLevel.info, "User logged in");
logger.log(LogLevel.debug, "Debugging x=42");
logger.log(LogLevel.trace, "Entered function foo()");

4. Configure log level in config/default.json:

{
	"log_level": "debug"
}

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Project Structure 🗂

HW3/
│
├─ index.ts               # Entry point, demonstrates usage
├─ Logger.ts              # Logger class implementation with LogLevel enum
├─ package.json           # NPM dependencies and scripts
├─ tsconfig.json          # TypeScript configuration
├─ config/
│   └─ default.json       # Configuration file with log_level
└─ logs.txt               # Example log output file

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Conclusion 🚀

This Logger provides a flexible and visually clear system for monitoring application events. It demonstrates the power of EventEmitter, TypeScript enums, and console formatting.

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Made with ❤️ and TypeScript by Sam-Shepsl Malikin