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Architectural Considerations for @hmlr/govuk-react-component-library

1. Component Architecture

1.1 Atomic Design Principles

  • Implement atomic design methodology to organize components.
  • Categorize components into atoms, molecules, organisms, templates, and pages.
  • Ensure each component is self-contained and reusable.

1.2 Component Structure

  • Each component should have its own directory containing:
    • Main component file (TSX)
    • Styles (SCSS)
    • Tests (TSX)
    • Stories (TSX)
    • Types (TSX)
    • Configuration (TSX)
  • Use index files for clean exports and imports.

1.3 Stateless vs. Stateful Components

  • Prefer stateless functional components where possible.
  • Use hooks for state management in functional components.
  • Limit the use of class components to scenarios where lifecycle methods are absolutely necessary.

2. State Management

2.1 Local State

  • Use React hooks (useState, useReducer) for component-level state management.
  • Avoid prop drilling by using context or state management libraries for deeply nested components.

2.2 Global State

  • Consider using React Context API for light global state management.
  • For more complex state requirements, integrate with external state management libraries like Redux or MobX.

3. Styling Architecture

3.1 CSS Methodology

  • Adopt a BEM (Block Element Modifier) naming convention for CSS classes.
  • Use SCSS for advanced styling features and better organization.

3.2 Theming

  • Implement a theming system using CSS variables or a styling solution like styled-components.
  • Ensure all components adhere to the GOV.UK Design System color palette and typography.

3.3 Responsive Design

  • Use mobile-first approach for responsive designs.
  • Implement flexible layouts using CSS Grid and Flexbox.

4. Performance Considerations

4.1 Code Splitting

  • Utilize dynamic imports and React.lazy for code splitting.
  • Implement route-based code splitting for larger applications using this library.

4.2 Memoization

  • Use React.memo for functional components to prevent unnecessary re-renders.
  • Implement useMemo and useCallback hooks to optimize performance in complex components.

4.3 Virtual DOM Optimization

  • Keep component trees shallow to optimize reconciliation.
  • Use keys properly in lists to help React identify which items have changed, been added, or been removed.

5. Accessibility (a11y)

5.1 ARIA Attributes

  • Implement proper ARIA roles, states, and properties in all components.
  • Ensure all interactive elements are keyboard accessible.

5.2 Color Contrast

  • Maintain WCAG 2.1 AA standard color contrast ratios.
  • Provide sufficient color contrast for text and important graphics.

5.3 Screen Reader Compatibility

  • Test all components with popular screen readers (NVDA, JAWS, VoiceOver).
  • Provide meaningful alt text for images and aria-label for interactive elements.

6. Testing Strategy

6.1 Unit Testing

  • Implement comprehensive unit tests for all components using Jest and React Testing Library.
  • Aim for high test coverage (>80%).

6.2 Integration Testing

  • Use Cypress or similar tools for integration testing.
  • Test component interactions and flows that span multiple components.

6.3 Visual Regression Testing

  • Implement visual regression tests using tools like Percy or Chromatic.
  • Ensure UI consistency across different browsers and devices.

7. Documentation

7.1 Storybook

  • Use Storybook for component documentation and visual testing.
  • Implement addons for accessibility checks, responsive views, and actions.

7.2 JSDoc

  • Use JSDoc comments for detailed documentation of component props, methods, and types.
  • Generate API documentation from JSDoc comments.

8. Build and Bundle

8.1 Module Formats

  • Support multiple module formats (CommonJS, ES modules) for maximum compatibility.
  • Use Rollup for efficient tree-shaking and smaller bundle sizes.

8.2 Optimization

  • Implement code minification and tree shaking in the build process.
  • Use babel-plugin-transform-react-remove-prop-types to remove PropTypes in production builds.

9. Versioning and Release Strategy

9.1 Semantic Versioning

  • Follow semantic versioning (SemVer) for releasing new versions.
  • Clearly document breaking changes in major version bumps.

9.2 Changelog

  • Maintain a detailed CHANGELOG.md file.
  • Use tools like conventional commits to automate changelog generation.

10. Internationalization (i18n)

10.1 Text Externalization

  • Externalize all user-facing strings for easy translation.
  • Use a i18n library like react-intl for managing translations.

10.2 RTL Support

  • Ensure components support right-to-left (RTL) languages.
  • Use logical properties (e.g., margin-inline-start instead of margin-left) for better RTL support.

11. Security Considerations

11.1 Input Sanitization

  • Implement proper input sanitization to prevent XSS attacks.
  • Use libraries like DOMPurify when rendering user-generated content.

11.2 Dependency Management

  • Regularly update dependencies to patch security vulnerabilities.
  • Use tools like npm audit to identify and fix security issues in dependencies.

These architectural considerations provide a comprehensive framework for developing and maintaining the @hmlr/govuk-react-component-library. They ensure the library is robust, performant, accessible, and aligned with modern React and web development best practices.

Architectural notes

Level 1: Context Diagram

The context diagram provides a high-level view of the system and its interactions with external entities.

  • System: HMLR React Components Library
    • Description: A library of React components based on GDS specifications for use in UK government digital services.
  • External Systems/Actors:
    • Developers: Use the library to build applications.
    • GitHub: Hosts the source code and manages version control.
    • GitLab CI/CD: Automates testing and deployment processes.
    • Users: End-users who interact with applications built using the library.

Level 2: Container Diagram

The container diagram shows the high-level technology choices and how the system is structured.

  • Containers:
    • React Components Library: The main codebase containing reusable React components.
      • Technologies: React, TypeScript, govuk-frontend
    • Storybook: A tool for developing and testing UI components in isolation.
      • Technologies: Storybook, React
    • CI/CD Pipeline: Automates testing and deployment.
      • Technologies: GitLab CI/CD, Docker
    • GitHub Pages: Hosts the Storybook for public access.
      • Technologies: GitHub Pages, gh-pages

Level 3: Component Diagram

The component diagram provides a more detailed view of the internal structure of the main container (React Components Library).

  • Components:
    • DateInput Component: A reusable date input field.
    • TaskList Component: A component for displaying task lists.
    • PDFViewerCanvas Component: A component for rendering PDF documents.
    • Utilities: Helper functions and utilities used across components.
    • Configuration: Configuration files for Babel, ESLint, and TypeScript.

Level 4: Code Diagram

The code diagram provides a detailed view of the internal structure of a specific component or module. This level is often represented by class diagrams or code snippets.

  • Example: DateInput Component
    • Files:
      • DateInput.tsx: The main component file.
      • DateInput.scss: Styles specific to the DateInput component.
      • DateInput.test.tsx: Test cases for the DateInput component.
      • DateInput.stories.tsx: Storybook stories for the DateInput component.