🕓 ofc-datetime

Lightweight, zero-dependency Date/Time utility library for fixed format (yyyy/MM/dd hh:mm:ss)
with UTC and Intl support for TypeScript.
by Kei Yusu (Oresama Foundation Code)

📦 Overview

ofc-datetime is a TypeScript utility library that provides simple and consistent date/time operations
without external dependencies.
It is part of the ofc (Oresama Foundation Code) utility series.

The library focuses on fixed-format date strings (yyyy/MM/dd hh:mm:ss)
to ensure predictable behavior across locales and environments.

⚙️ Features

• ✅ Zero dependency — lightweight and portable
• 🕰 Supports both local and UTC calculations
• 🌍 Includes Intl (internationalization) support
• 🧮 Provides unified functions for:
  • Date/time conversion
  • Format validation
  • Arithmetic (add/subtract)
  • Difference calculation (day/hour/minute/second/millisecond)
  • Decomposition (divideDateTime)
  • Reconstruction (makeDateTimeString)
• 🧪 90%+ test coverage using Jest

📘 Installation

npm install @kyusu/ofc-datetime

or for development:

npm install @kyusu/ofc-datetime --save-dev

🚀 Usage

import { 
  getNowDateString, 
  toDateString, 
  addDays, 
  diffHour,
  divideDateTime 
} from "@kyusu/ofc-datetime";

// Get current date
console.log(getNowDateString()); // "2025/11/08"

// Format conversion
console.log(toDateString("20251108")); // "2025/11/08"

// Add days
console.log(addDays("2025/11/08 00:00:00", 5)); // "2025/11/13 00:00:00"

// Calculate difference (in hours)
console.log(diffHour("2025/11/08 00:00:00", "2025/11/09 06:00:00")); // 30

// Split datetime string into components
console.log(divideDateTime("2025/11/08 13:02:10"));
// → { y:2025, m:11, d:8, hr:13, min:2, sec:10 }

🧩 Function Categories

| Category | Description | Example Functions | |-----------|--------------|-------------------| | Current Date/Time | Now-local, UTC, Intl | getNowDateString(), getNowDateTimeStringUTC() | | Format Conversion | Convert between numeric & formatted strings | toDateString(), toNumberTimeString() | | Validation | Format / range validation | isDateValid(), isDateTimeValid() | | Arithmetic (Add) | Add years, months, days, etc. | addDays(), addSecondsUTC() | | Difference (Diff) | Calculate elapsed time | diffHour(), diffMinuteUTC() | | Elapsed Time (Past) | Full difference breakdown | pastDateTime() | | Split / Compose | Break or reconstruct datetime strings | divideDateTime(), makeDateTimeString() |

🧪 Testing

Run all tests:

npm test

Generate coverage report (HTML):

npm run test:coverage

Coverage output (local only):

coverage/lcov-report/index.html

📁 Project Structure

ofc-datetime/
├── src/
│   └── ofcDateTime.ts
├── tests/
│   └── ofcDateTime.test.ts
├── dist/
│   ├── ofcDateTime.js
│   ├── ofcDateTime.d.ts
│   └── ofcDateTime.js.map
├── package.json
├── tsconfig.json
└── jest.config.js

📘 Documentation

• API Reference (English)
• APIリファレンス（日本語）

🔒 License

MIT © Kei Yusu
Part of the Oresama Foundation Code series.

🌐 Links

• GitHub: https://github.com/kyusu0918/ofc-datetime
• Author: Kei Yusu（@kyusu0918）
• Series: Oresama Foundation Code

“Simple, predictable, and fully typed date/time utilities — that’s all you need.”