SimpleCalculator

A lightweight calculator with a vanilla JavaScript frontend and Express.js backend. Works fully offline by default, with optional cloud sync to persist calculation history across devices.

Features

Core Calculator

• Standard arithmetic operations with sequential expression evaluation
• Responsive, keyboard-accessible interface
• Local calculation history with delete and reset controls
• Input validation and comprehensive error handling

Optional Cloud Sync

• Session-based authentication using username and sync key
• Persist history to the cloud and access it from any device
• Clear synced history and revoke active sessions on demand

Tech Stack

Area	Technologies
Frontend	HTML5, CSS3, Vanilla JavaScript
Backend	Node.js, Express.js, SQLite, Drizzle ORM
Security	bcrypt-ts, CORS, dotenv
Architecture	Layered: Routes → Controllers → Services → Database

Project Structure

simpleCalculator/
├── frontend/
│   ├── assets/
│   ├── css/
│   ├── js/
│   ├── history/
│   └── index.html
├── backend/
│   ├── src/
│   ├── drizzle.config.js
│   ├── package.json
│   └── sqlite.db
└── README.md