React

React Core Patterns

When to Use

• Creating React components
• Working with hooks (useState, useEffect, custom hooks)
• Implementing Suspense boundaries
• Setting up lazy loading with React.lazy
• Using React 19 patterns (ref as prop, no forwardRef)
• Structuring component files
• Optimizing component performance

Purpose

Essential React 19 patterns for building modern applications with hooks, Suspense, lazy loading, and TypeScript.

Note: DSAI Component Convention (React 19):

• forwardRef is REQUIRED for all DSAI components — use memo(forwardRef(function Name(props, ref))) pattern
• Every component MUST have a displayName property
• Props go in separate *.types.ts files
• propTypes removed (use TypeScript interfaces)
• New JSX transform required
• React.FC type discouraged — use direct function components with typed props

When to Use This Skill

• Creating React components
• Using React hooks (useState, useEffect, useCallback, useMemo)
• Implementing lazy loading and code splitting
• Working with Suspense boundaries
• React-specific TypeScript patterns
• Performance optimization with React

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Quick Start

Component Structure Template

import { forwardRef, memo, useState, useCallback } from 'react';
import { cn } from '@/lib/utils';
import type { UserProfileProps } from './UserProfile.types';

// Props defined in UserProfile.types.ts:
// interface UserProfileProps {
//   userId: string;
//   onUpdate?: (data: UserData) => void;
//   className?: string;
// }

export const UserProfile = memo(
  forwardRef<HTMLDivElement, UserProfileProps>(
    function UserProfile({ userId, onUpdate, className }, ref) {
      const [data, setData] = useState<UserData | null>(null);

      const handleUpdate = useCallback((newData: UserData) => {
        setData(newData);
        onUpdate?.(newData);
      }, [onUpdate]);

      return (
        <div ref={ref} className={cn('user-profile', className)}>
          {/* Component content */}
        </div>
      );
    }
  )
);
UserProfile.displayName = 'UserProfile';

Component Checklist

Creating a React component? Follow this:

• Use memo(forwardRef(function Name(props, ref))) pattern
• Set displayName on every component
• Props in separate *.types.ts file
• Use cn() for class name composition (Bootstrap classes, not Tailwind)
• Use useCallback for event handlers passed to children
• Use useMemo for expensive computations
• Lazy load if heavy component: lazy(() => import())
• Wrap lazy components in <Suspense> with fallback
• Named export only (no default exports)
• No conditional hooks (hooks must be called in same order)
• Import from @/components/ui/ for DSAI components

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Core Hooks Patterns

See hooks-patterns.md for useState, useCallback, useMemo, and useEffect patterns with TypeScript examples.

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Lazy Loading & Code Splitting

See lazy-loading.md for React.lazy, Suspense fallbacks, and feature-based code splitting examples.

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Suspense Patterns

Suspense Boundaries

// Wrap data-fetching components
<Suspense fallback={<Skeleton />}>
  <UserProfile userId={id} />
</Suspense>

// Nested Suspense for granular loading
<Suspense fallback={<PageLoader />}>
  <Header />
  <Suspense fallback={<ContentSkeleton />}>
    <MainContent />
  </Suspense>
  <Footer />
</Suspense>

Error Boundaries with Suspense

import { ErrorBoundary } from 'react-error-boundary';

<ErrorBoundary fallback={<ErrorFallback />}>
  <Suspense fallback={<Loading />}>
    <DataComponent />
  </Suspense>
</ErrorBoundary>

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TypeScript Patterns

See typescript-patterns.md for component props, hooks typing, and custom hook return types.

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Performance Optimization

See performance.md for React.memo usage, custom comparison functions, and avoiding re-renders.

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Common Patterns

Conditional Rendering

// Ternary operator
{isLoading ? <Spinner /> : <Content />}

// Logical AND
{error && <ErrorMessage error={error} />}

// Nullish coalescing
{user ?? <GuestView />}

// Early return for loading states
function Component() {
  const { data } = useSomeHook();

  // ❌ Avoid early returns for loading - breaks hooks rules
  // Use Suspense instead

  return <div>{data.map(...)}</div>;
}

Lists and Keys

// Always use stable keys
{items.map(item => (
  <ItemCard key={item.id} item={item} />
))}

// Never use index as key if list can reorder
// ❌ Bad
{items.map((item, index) => (
  <ItemCard key={index} item={item} />
))}

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File Organization

Feature-Based Structure

src/client/
├── components/
│   ├── ui/              # DSAI components (installed via `dsai add`)
│   │   ├── button/
│   │   │   ├── Button.tsx
│   │   │   ├── Button.types.ts
│   │   │   ├── Button.fsm.ts
│   │   │   └── index.ts
│   │   ├── modal/
│   │   └── card/
│   └── features/        # App-specific feature components
│       ├── auth/
│       └── posts/
├── hooks/               # Shared hooks (DSAI + custom)
├── lib/
│   └── utils/           # Utilities (cn, validators, etc.)
└── types/               # Shared types

Component Co-location

components/ui/button/
├── Button.tsx           # Component with forwardRef + displayName
├── Button.types.ts      # TypeScript prop interfaces
├── Button.fsm.ts        # FSM reducer (interactive components)
├── Button.test.tsx       # Unit tests (Jest 30 + RTL)
├── Button.a11y.test.tsx  # Accessibility tests (jest-axe)
└── index.ts             # Barrel exports

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Common Mistakes to Avoid

See common-mistakes.md for conditional hooks, missing dependencies, and state mutation anti-patterns.

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Additional Resources

For more detailed patterns, see:

• component-patterns.md - Advanced component patterns
• performance.md - Performance optimization techniques
• typescript-patterns.md - TypeScript best practices
• hooks-patterns.md - Custom hooks and advanced patterns