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name: development description: Core development standards, patterns, and best practices for React and React Native projects. Use this when users need guidance on code quality (Biome, TypeScript), testing (Jest), project structure (Domain-Driven Design), React best practices (useEffect guidelines), or React Native development with Expo. license: MIT - Complete terms in LICENSE.txt

Development Skills & Best Practices

Core development standards, patterns, and best practices for React and React Native projects.

Table of Contents

• Code Quality & Linting
• Testing
• Project Structure
• React Best Practices
• React Native

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Code Quality & Linting

Biome

• MUST use Biome (latest stable) for both linting and code formatting - this is a strict requirement
• Configure Biome with project-specific rules
• Use Biome's built-in formatter (no need for Prettier or ESLint)
• Run linting and formatting checks in CI/CD pipeline
• Ensure consistent code style across the team
• MUST format code with Biome before committing - this is a strict requirement
• MUST run linting checks before committing - this is a strict requirement

TypeScript

• MUST use TypeScript (latest stable, 5.x) with strict mode enabled - this is a strict requirement
• PREFER configuring strict TypeScript settings for maximum type safety (guideline)
• Run tsc type checking in pre-push hooks
• Include TypeScript checks in CI pipeline
• MUST avoid using any type - use proper types or unknown when necessary - this is a strict requirement

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Testing

Jest

• MUST use Jest (latest stable) as the testing framework for all projects - this is a strict requirement
• Write unit tests for all business logic and utilities
• Write integration tests for critical user flows
• Aim for meaningful test coverage (focus on quality over quantity)
• PREFER using React Testing Library for component testing (guideline)
• Mock external dependencies and APIs appropriately
• Keep tests fast, isolated, and maintainable

Test Structure

• PREFER placing test files next to the code they test (co-location) - this is a guideline
• Use descriptive test names that explain what is being tested
• PREFER following the Arrange-Act-Assert pattern (guideline)
• Use describe blocks to group related tests
• Run tests in watch mode during development

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Project Structure

Domain-Driven Design

• PREFER using Domain-Driven Design (DDD) principles for project structure (guideline)
• Organize code by domain/feature rather than by technical layer
• Each domain should be self-contained with its own:
  • Components
  • Hooks
  • Utilities
  • Types
  • Tests

Example Structure:

Copysrc/
  domains/
    auth/
      components/
      hooks/
      utils/
      types/
      __tests__/
    user/
      components/
      hooks/
      utils/
      types/
      __tests__/
  shared/
    components/
    hooks/
    utils/
    types/
  app/
    layout.tsx
    page.tsx

Benefits:

• Better code organization and discoverability
• Easier to scale and maintain
• Clear boundaries between features
• Facilitates team collaboration

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React Best Practices

useEffect Guidelines

MUST follow React's official guidance: You Might Not Need an Effect - this is a strict requirement

Key Principles (Strict Requirements):

1. MUST NOT use Effects for data transformation - this is a strict requirement

   • Calculate derived values during rendering
   • Use useMemo for expensive calculations
   • Avoid redundant state variables

2. MUST NOT use Effects for user events - this is a strict requirement

   • Handle user interactions in event handlers
   • Effects should only synchronize with external systems

3. When to use Effects:

   • Synchronizing with external systems (browser APIs, third-party libraries)
   • Data fetching (though modern frameworks provide better alternatives)
   • Subscribing to external stores

4. Best Practices:

   • MUST always include cleanup functions for subscriptions - this is a strict requirement
   • Handle race conditions in data fetching
   • Extract data fetching logic into custom hooks
   • Prefer server components and React Server Actions when possible

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React Native

Expo Framework

• MUST use Expo SDK 54.x for all React Native projects - this is a strict requirement
• Leverage Expo's managed workflow for easier development
• Use Expo SDK for native module access
• Follow Expo's best practices for app configuration

Creating a New Expo App with TypeScript

To create a new React Native Expo app with TypeScript and the tabs template:

Copynpx create-expo-app@latest my-app --template tabs

Replace my-app with your desired project name. The tabs template includes:

• TypeScript configuration
• Expo Router with tab navigation
• Pre-configured navigation structure

Alternative templates:

• blank-typescript - Minimal TypeScript template
• blank - Minimal JavaScript template
• tabs - Tab navigation with TypeScript (recommended)

For more information, see the Expo Documentation.

Initial Project Setup

After creating a new React Native Expo app, immediately install and configure:

1. Biome - For linting and code formatting
2. Lefthook - For Git hooks to enforce code quality

These tools should be set up before any significant development begins to ensure code quality from the start.

Git Commit Practices

• Commit often and logically - Make small, focused commits that represent logical units of work
• Fix linting errors before committing - Since Lefthook runs linting on pre-commit/pre-push hooks, all linting errors must be resolved before the commit can proceed
• Quality is essential - Never bypass or skip linting checks. Fix errors until they are resolved
• Each commit should be meaningful and pass all quality checks

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Additional Resources

• React Documentation - You Might Not Need an Effect
• Expo Documentation
• Biome Documentation
• Jest Documentation
• TypeScript Documentation
• Domain-Driven Design

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Notes

• This document should be reviewed and updated regularly as best practices evolve
• Team-specific additions and modifications are encouraged
• When in doubt, refer to official documentation and community standards