Point of Sale: Building a Retail POS System
Why Build a POS?
Small shops in Nairobi often use either pen-and-paper or expensive proprietary POS systems. I wanted to build an accessible, web-based alternative that runs on any device with a browser — no special hardware required.
Tech Stack
- JavaScript — frontend and backend logic
- HTML/CSS — responsive cashier interface
- Local Storage / IndexedDB — offline-capable data persistence
Core Features
Product Catalog
Products are stored with name, SKU, price, and current stock quantity. The catalog supports search-as-you-type for quick product lookup during checkout.
Cart System
A drag-and-click cart system where cashiers can add items, adjust quantities, apply discounts, and see running totals. The cart persists across page refreshes so accidental navigation doesn't lose a sale.
Receipt Generation
After checkout, the system generates a formatted receipt that can be printed or sent digitally. Receipts include itemized lists, taxes, payment method, and change due.
Basic Inventory
Stock levels automatically decrement when a sale is completed. Low-stock alerts notify the shop owner when items need reordering.
Design for Speed
A cashier's primary need is speed. Every interaction was optimized for minimal clicks:
- Keyboard shortcuts for common actions (Enter to add, Esc to clear)
- Large touch targets for mobile/tablet use
- Instant search — no "Search" button, results appear as you type
Challenges
The hardest part was handling offline scenarios. Shops in some areas have unreliable internet. I implemented a queue-based sync system: sales are recorded locally and synced to the server when connectivity returns. Conflict resolution (e.g., inventory mismatch) was the trickiest edge case.