Non-Functional Requirements

⚙️ Step 2: Non-Functional Requirements – E-commerce App

Beyond features, a good frontend system is defined by its quality attributes — how fast, accessible, secure, and maintainable it is.

Here are the key non-functional goals for our Angular-based e-commerce store:

🚀 Performance

• Use lazy loading for feature modules like cart, wishlist, and checkout.
• Apply OnPush change detection to optimize rendering.

📱 Responsiveness

• Implement a mobile-first layout with CSS Flex/Grid.
• Use Angular’s BreakPointObserver if needed for dynamic layouts.

🔒 Security

• Avoid XSS using Angular's built-in sanitization.
• Protect routes with guards (auth, roles).
• Store JWT securely (prefer HttpOnly cookie strategy).

♿ Accessibility

• Follow WCAG 2.1 guidelines.
• Use ARIA labels and proper semantic HTML.
• Ensure full keyboard navigation (especially for product filters and checkout forms).

These NFRs guide every future design decision — from component strategy to folder structure, from routing to testing.

🧱 Reliability

• Graceful fallback UIs for failed API calls (e.g., show error messages, retry options, empty state UI).
• Use RxJS retry/backoff patterns for network resilience where appropriate.
• Critical flows like checkout, cart updates, and login include optimistic updates with rollback handling.
• Monitor key events via custom error handlers and global interceptors.
• Detect and alert runtime errors using tools like Sentry, Firebase Crashlytics, or custom logging.

🧪 Combine with testing strategy to catch regressions early and ensure uptime through reliable user experiences.

📈 Scalability

• Modular architecture using feature-based folders (e.g., /products, /cart, /orders) allows easy onboarding of new features.
• State is managed centrally using NgRx or locally via Signals, enabling distributed development and horizontal scaling.
• Feature modules are lazy loaded, ensuring performance even as the app grows.
• Ready for micro frontends if needed in the future (e.g., separate admin panel, product engine, etc.).

🛠️ Maintainability

• Uses DRY (Don't Repeat Yourself) principles via shared components, pipes, and services.
• Follows Angular style guide: consistent naming, smart/dumb component separation, clear folder structure.
• Includes CoreModule for singleton services and SharedModule for UI elements to reduce duplication.
• Encourages single responsibility principle (SRP) for services and components.

🧪 Testing Strategy

• Write unit tests for every service and pipe.
• Cover component outputs and user interactions via integration tests.
• Run E2E tests for cart, checkout, and auth flows.
• Use TestBed for isolation and mocking dependencies.

🔁 Automated testing in CI pipelines is recommended for consistent build verification.

✅ These additions ensure that your e-commerce frontend isn’t just feature-complete, but also engineered to last — flexible to scale, easy to modify, and reliable in real-world use.