Online Calculator (Frontend + Backend)

An online calculator with:

• Basic calculator UI (client-side)
• Safe server-side evaluation via mathjs
• Image upload + OCR (Tesseract.js) to extract and solve expressions from pictures
• Notes feature with simple file persistence

Project Structure

• backend/
  • Express server, file uploads, OCR, notes persistence
• frontend/
  • React app (CRA structure)

Prerequisites

• Node.js 18+ and npm

Setup & Run (Development)

Open two terminals.

Terminal 1 (Backend):

npm install
npm run dev

Run these in the backend/ directory.

Terminal 2 (Frontend):

npm install
npm start

Run these in the frontend/ directory. The React dev server proxies API calls to http://localhost:5000.

API Overview (Backend)

• POST /calculate { expression: string }
  • Returns { result, expression } using mathjs.
• POST /upload (form-data: image)
  • Uploads an image and returns metadata.
• POST /solve-image (form-data: image)
  • Runs OCR to extract a math expression and returns { recognizedText, expression, result }.
• GET /notes
  • List all notes.
• POST /notes { title, content }
  • Create a note.
• DELETE /notes/:id
  • Delete a note by id.

Notes Storage

Notes are persisted to backend/data/notes.json. Uploads are stored in backend/uploads/.

Security Notes

• Expression evaluation uses mathjs. Avoid evaluating untrusted input outside of allowed mathjs scope.
• File uploads limited to images and 10 MB. Adjust as needed in backend/server.js.

Troubleshooting

• If OCR is slow on first run, Tesseract will download language data. Internet access is required.
• On Windows camera access, ensure the browser has permission and the device has a camera.

License

MIT