architecture

Architecture Skill

Applicability

• Platforms: iOS and Android
• React Native: 0.76+ (New Architecture interop assumed unless a checklist item says otherwise)

When to Use

• Designing the folder and module structure for a new feature
• Reviewing a pull request for structural or navigation issues
• Adding deep links or wiring screens into navigation
• Isolating crashes so one feature cannot take down the whole app
• Checking general code quality before merge

Guidance

Feature Structure

• Feature sits in its own folder (src/features/{name}/)
• No cross-feature imports (share only through a shared/ module)
• Barrel export (index.ts) only exposes the feature's public API
• No business logic in components — extract to hooks and utilities
• Clear separation: screen (layout) vs components (reusable UI) vs hooks (logic)

Navigation & Deep Linking

• Screen registered in navigation with type-safe params
• Deep link configured for every navigable screen
• Deep link handles both cold start and background resume (different lifecycles)
• Deep links to authenticated screens check auth state first
• Expired or invalid deep link content handled gracefully
• Navigation params treated as optional and validated
• Back button goes to the expected screen
• Navigation stack reset on sign-out (no deep-linking back into authenticated content)

Incorrect:

const { itemId } = route.params; // crashes if params undefined
const item = useItem(itemId);

Correct:

const itemId = route.params?.itemId;
if (!itemId) return <ErrorScreen message="Invalid link" />;
const item = useItem(itemId);

Rendering Safety

• Conditional rendering handles falsy values correctly
• Components return null, not undefined, for an empty render
• List items have stable, unique keys (not array index)

Incorrect:

{count && <Text>{count} items</Text>}        // renders "0" when count is 0
<Text>Hello {user.name}</Text>               // crashes on Android if name is undefined

Correct:

{count > 0 && <Text>{count} items</Text>}
<Text>Hello {user?.name ?? 'Guest'}</Text>

Resilience & Error Boundaries

• Error boundary at the app root and one per feature (crash isolated to feature)
• Graceful degradation: disable a feature rather than crash the app
• Errors are never swallowed silently
• Fallback UI is simple enough to never crash itself (no API calls, no complex state)

Incorrect:

export default function App() {
  return <Navigator />; // one crash anywhere kills the entire app
}

Correct:

export default function App() {
  return (
    <ErrorBoundary fallback={<AppCrashScreen />}>
      <Navigator />
    </ErrorBoundary>
  );
}

function SearchScreen() {
  return (
    <ErrorBoundary fallback={<SearchUnavailable />}>
      <SearchContent />
    </ErrorBoundary>
  );
}

Code Quality

• TypeScript: no any, no @ts-ignore without an explanation
• No console.log left in (use a proper logging utility)
• No commented-out code committed
• No TODO without a linked ticket
• Component props have a named TypeScript interface (not inline)
• Files stay under ~300 lines; functions under ~50 lines (split when larger)

Anti-Patterns

Anti-Pattern	Why It's Bad	Fix
Cross-feature imports	Tight coupling, hard to move or delete features	Share through shared/ only
navigate called during render	Infinite loop	Move to useEffect or an event handler
Components defined inside components	Re-mounts every render, loses state	Define at module scope
Platform checks scattered everywhere	Hard to follow, easy to miss a case	Use .ios.ts / .android.ts files
any type	Defeats TypeScript, hides bugs	Use proper types or unknown
Missing error boundary	One crash takes down the whole app	Error boundary per feature

Pitfalls

• Error boundaries only catch render and lifecycle errors — not errors in event handlers or async code. Handle those explicitly.
• Deep links fire on both cold start and background resume; the two paths have different lifecycles and both need testing.
• undefined rendered inside <Text> crashes on Android but silently works on iOS, so iOS-only testing misses it.
• Using array index as a list key causes the wrong items to re-render on reorder or delete.