Homework 2: Code and Comment Extractor 📝

🧩 Task Definition

The goal of this homework is to create a Node.js application that separates TypeScript code from comments in a given source file.

The application must:

• Read an input TypeScript file line-by-line.
• Split each line into code and comment parts.
• Write two separate output files:
  • One containing only the code.
  • One containing only the comments.
• Support comments starting with // (single-line comments).

Example

Input file:

//abcd is a variable of type number
let abcd: number;
const lmn = 5; //constant lmn contains value 5

Output code file:

let abcd: number;
const lmn = 5;

Output comment file:

//abcd is a variable of type number
//constant lmn contains value 5

Paths to the input and output files must be configured in the config module.

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📝 Description

This project is a TypeScript Node.js application designed to parse source files and extract comments and code into separate files.
It uses asynchronous file reading with Node.js streams and the readline module for line-by-line processing.

The main modules are:

• CommentParser — responsible for splitting code and comments from each line.
• FileHandler — responsible for reading input files and writing output files.
• config — stores paths for input and output files.

The project also includes unit tests with Jest to ensure the parsing logic works correctly.

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🎯 Purpose

This project helps to:

• Practice file handling and stream processing in Node.js.
• Learn line-by-line parsing using readline.
• Apply string manipulation and parsing logic in TypeScript.
• Set up a modern TypeScript project with ESM modules.
• Configure and run unit tests with Jest and ts-jest.

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🔍 How It Works

1. The application reads the input file asynchronously.
2. Each line is sent to CommentParser.extractCodeAndComments():
   • Lines starting with // are considered comments only.
   • Lines containing both code and comment are split at the first occurrence of //.
   • Lines without // are treated as code only.
3. Extracted code lines and comment lines are collected in arrays.
4. FileHandler writes these arrays into separate files defined in the configuration.
5. Logging is performed for process tracking and error handling.

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📜 Output Example

Input file:

const x = 5; // это переменная
let y = 10;
// комментарий

Generated output files:

• Code output file:

const x = 5;
let y = 10;

• Comment output file:

// это переменная
// комментарий

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📦 Usage

1. Clone the repository:

git clone <repo-url>
cd HW2

2. Install dependencies:

npm install

3. Configure file paths in config/default.json:

{
	"inputFilePath": "./input.txt",
	"outputCodeFilePath": "./output_code.txt",
	"outputCommentFilePath": "./output_comments.txt"
}

4. Run the application:

npm start

5. Run tests:

npm test

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🗂 Project Structure

HW2/
│
├── src/
│   ├── app.ts                 # Main application entry point
│   ├── parser/
│   │   └── CommentParser.ts  # Logic for extracting code and comments
│   └── utils/
│       └── FileHandler.ts    # File reading/writing utilities
│
├── tests/
│   ├── CommentParser.test.ts
│   └── FileHandler.test.ts
│
├── config/
│   └── default.json          # Configuration for input/output file paths
│
├── jest.config.cjs           # Jest configuration for ts-jest with ESM
├── package.json
├── tsconfig.json
└── README.md

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🧪 Testing

Unit tests verify:

• Correct splitting of code and comments in all scenarios:
  • Comment-only lines
  • Code-only lines
  • Lines with code and inline comments
• Correct handling of empty lines
• Proper writing of output files

Run tests with:

npm test

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✅ Dependencies

• Node.js 18+
• TypeScript
• Jest (ts-jest)

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🚀 Conclusion

This project demonstrates:

• Asynchronous file reading and writing in Node.js
• Line-by-line parsing and string manipulation in TypeScript
• Separation of code and comments for analysis or documentation purposes
• Unit testing with Jest in a TypeScript environment

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Made with ❤️ and TypeScript by Sam-Shepsl Malikin