🧮 Calculator

Web calculator with persistent history, virtual keypad, and keyboard shortcuts. Expression evaluation via a custom parser (no eval).

📦 Installation

npm install

Requirements: Node ^20.19.0 or >=22.12.0.

▶️ Running

npm run dev       # development server
npm run build     # production build
npm run test:unit # unit tests

🧩 Features

✅ Input and calculation

• Expression field — Type or use the virtual keypad. Accepts spaces; known characters are normalized (e.g. * → ×).
• Operators: addition (+), subtraction (−), multiplication (×), division (÷), square (²), percent (%), and parentheses. Decimal numbers with a dot.
• Precedence: multiplication and division before addition and subtraction; parentheses override the order.
• = / Enter — Evaluates, shows the result in the field, and adds it to history.

✅ Keypad

• Virtual keypad — Buttons for digits, operators, parentheses, C (clear), ., %, ², etc. Double × inserts ².
• Physical keyboard — Outside the field: mapped digits and operators, Enter/= to evaluate, Backspace to remove the last character. Inside the field: normal typing and paste; Enter evaluates.

✅ History

• Calculation list — Each row shows expression and result. Click a row to reuse that expression.
• Delete item — Hover over a row to show the delete button; click to remove it from history.
• Clear All — Top button clears the entire history.
• Persistence — History is stored in the browser (localStorage) across sessions.

✅ Errors

• Error messages (invalid expression, division by zero, unbalanced parentheses, etc.) appear above the field. Any new edit or action clears the error.

⚙️ Technical stack

• Frontend: Vue 3 (Composition API), TypeScript.
• State: Pinia with history persistence (pinia-plugin-persistedstate).
• Styling: Tailwind CSS v4.
• Build: Vite 7.
• Tests: Vitest and Vue Test Utils (store, expression evaluator, clicks, keyboard, and history).
• Expression evaluation: Custom parser (tokenization + precedence), no eval. Supports +, −, ×, ÷, ², %, and parentheses.

🧩 Benefits

✅ Persistent history in the browser
✅ Input via virtual and physical keyboard
✅ Safe expression parser (no eval)
✅ Operator precedence and parentheses
✅ Unit tests (store, eval, UI, and keyboard)