Expo Architecture Guidelines

References

Consult these resources for detailed implementation patterns:

• ./references/folder-structure.md -- Deep dive into the src/ directory organization.
• ./references/state-management.md -- Best practices for Jotai atoms and persistence.
• ./references/component-standards.md -- Standards for UI components, styling, and testing.

This document outlines the architectural patterns and technical standards used in this boilerplate.

Architecture Overview

The project follows a modular architecture that separates concerns into clear layers:

• Presentation Layer: React components and Expo Router screens.
• State Management Layer: Atoms (Jotai) and Stores.
• Service Layer: API clients and HTTP abstractions.
• Data Layer: Models (Types) and Mocks.
• Utility Layer: Helper functions and cross-cutting concerns.
• Design System: Theme-based styling and design tokens.

Folder Structure (src/)

• app/: Expo Router routes and layouts. Handles file-based navigation.
• components/: Reusable UI components. Each component should be in its own folder.
• constants/: Global constants (Environment variables, Storage keys, Strings).
• hooks/: Custom React hooks for shared logic.
• models/: TypeScript interfaces and types (Data models).
• services/: API integration and external service handlers.
• stores/: Jotai atoms for global and persistent state.
• styles/: Global styles and styled-component-like abstractions.
• tasks/: Background tasks and cron-like jobs.
• theme/: Design tokens (Colors, Spacing, Fonts, Opacity, Border).
• utils/: Low-level utility functions (Storage, Cache, Matchers).

State Management (Jotai)

We use Jotai for atomic state management.

• Atoms: Define atoms in src/stores/.
• Naming: Use Atom suffix for atom variables (e.g., articlesAtom).
• Persistence: Use atomWithStorage for data that should persist across app reloads.
• Computed Atoms: Use read-only or read-write atoms for derived state to keep logic out of components.

Example:

import { atom } from 'jotai';
import { atomWithStorage } from 'jotai/utils';

export const countAtom = atom(0);
export const persistentCountAtom = atomWithStorage('count', 0);

Component Pattern

Each component should follow the "Folder-per-Component" pattern:

src/components/MyComponent/
├── MyComponent.tsx           # Implementation
├── MyComponent.styles.ts     # StyleSheet definitions
├── MyComponent.stories.tsx    # Storybook documentation
└── MyComponent.test.tsx      # Unit tests (Co-located)

• Styling: Always separate styles from implementation using .styles.ts.
• Theme: Use the theme() function from @/theme/colors inject colors.
• PascalCase: Folders and implementation files must use PascalCase (e.g., AppBar.tsx).
• Co-location: Keep tests and stories next to the code.

Service Layer

• HTTP Client: Use the abstracted http utility for base requests.
• API Services: Define business-specific API calls in src/services/api.ts.
• Mocks: Store mock data in src/services/mocks/ for development and testing.

Routing (Expo Router)

• Keep app/ files lean. Delegate logic to hooks or stores.
• Use _layout.tsx for shared UI (Headers, Providers, Sidebars).
• Use Slot or Stack depending on the navigation needs.

Code Standards

• Formatting: We use Biome. Run bun format to ensure code style compliance.
• TypeScript: Use path aliases (@/) to avoid deep relative paths (e.g., ../../../../utils).
• Unit Testing:
  • Mandatory for components with logic, hooks, and stores.
  • Follow EXPO-TEST-SETUP.instructions.md.
  • Use @testing-library/react-native.

Design System

• Do not use hardcoded colors. Use theme() from src/theme/colors.ts.
• Use design tokens from src/theme/ (spacing, fonts, etc.) for consistency.
• Prefer expo-image over native Image for better caching and performance.