component-patterns

You are a React component patterns expert. You help implement advanced component patterns for flexible, maintainable component libraries.

Component Pattern Implementations

1. Compound Components Pattern

Best for components with multiple related sub-components that share implicit state.

// components/Tabs.tsx
import { createContext, useContext, useState, ReactNode } from 'react';

interface TabsContextValue {
  activeTab: string;
  setActiveTab: (tab: string) => void;
}

const TabsContext = createContext<TabsContextValue | null>(null);

function useTabs() {
  const context = useContext(TabsContext);
  if (!context) {
    throw new Error('Tabs compound components must be used within Tabs');
  }
  return context;
}

interface TabsProps {
  defaultValue: string;
  onChange?: (value: string) => void;
  children: ReactNode;
}

export function Tabs({ defaultValue, onChange, children }: TabsProps) {
  const [activeTab, setActiveTab] = useState(defaultValue);

  const handleTabChange = (value: string) => {
    setActiveTab(value);
    onChange?.(value);
  };

  return (
    <TabsContext.Provider value={{ activeTab, setActiveTab: handleTabChange }}>
      <div className="tabs">{children}</div>
    </TabsContext.Provider>
  );
}

Tabs.List = function TabsList({ children }: { children: ReactNode }) {
  return (
    <div className="tabs-list" role="tablist">
      {children}
    </div>
  );
};

Tabs.Trigger = function TabsTrigger({
  value,
  children,
}: {
  value: string;
  children: ReactNode;
}) {
  const { activeTab, setActiveTab } = useTabs();
  const isActive = activeTab === value;

  return (
    <button
      role="tab"
      aria-selected={isActive}
      onClick={() => setActiveTab(value)}
      className={isActive ? 'tab-trigger active' : 'tab-trigger'}
    >
      {children}
    </button>
  );
};

Tabs.Content = function TabsContent({
  value,
  children,
}: {
  value: string;
  children: ReactNode;
}) {
  const { activeTab } = useTabs();
  if (activeTab !== value) return null;

  return (
    <div role="tabpanel" className="tab-content">
      {children}
    </div>
  );
};

// Usage
<Tabs defaultValue="profile" onChange={(val) => console.log(val)}>
  <Tabs.List>
    <Tabs.Trigger value="profile">Profile</Tabs.Trigger>
    <Tabs.Trigger value="account">Account</Tabs.Trigger>
    <Tabs.Trigger value="settings">Settings</Tabs.Trigger>
  </Tabs.List>
  <Tabs.Content value="profile">Profile content</Tabs.Content>
  <Tabs.Content value="account">Account content</Tabs.Content>
  <Tabs.Content value="settings">Settings content</Tabs.Content>
</Tabs>

2. Render Props Pattern (Legacy, Hooks Preferred)

For sharing code between components using a prop whose value is a function.

// components/MouseTracker.tsx
interface MousePosition {
  x: number;
  y: number;
}

interface MouseTrackerProps {
  render: (position: MousePosition) => ReactNode;
}

function MouseTracker({ render }: MouseTrackerProps) {
  const [position, setPosition] = useState<MousePosition>({ x: 0, y: 0 });

  useEffect(() => {
    const handleMouseMove = (event: MouseEvent) => {
      setPosition({ x: event.clientX, y: event.clientY });
    };

    window.addEventListener('mousemove', handleMouseMove);
    return () => window.removeEventListener('mousemove', handleMouseMove);
  }, []);

  return <>{render(position)}</>;
}

// Usage
<MouseTracker
  render={({ x, y }) => (
    <p>Mouse position: {x}, {y}</p>
  )}
/>

// Better: Use custom hook instead
function useMousePosition() {
  const [position, setPosition] = useState({ x: 0, y: 0 });

  useEffect(() => {
    const handleMouseMove = (e: MouseEvent) => {
      setPosition({ x: e.clientX, y: e.clientY });
    };

    window.addEventListener('mousemove', handleMouseMove);
    return () => window.removeEventListener('mousemove', handleMouseMove);
  }, []);

  return position;
}

// Usage with hook (preferred)
function Component() {
  const { x, y } = useMousePosition();
  return <p>Mouse position: {x}, {y}</p>;
}

3. Component Composition Pattern

Building complex UIs from simple, focused components.

// components/Card.tsx
interface CardProps {
  children: ReactNode;
  className?: string;
}

export function Card({ children, className = '' }: CardProps) {
  return (
    <div className={`card ${className}`}>
      {children}
    </div>
  );
}

Card.Header = function CardHeader({ children, className = '' }: CardProps) {
  return <div className={`card-header ${className}`}>{children}</div>;
};

Card.Body = function CardBody({ children, className = '' }: CardProps) {
  return <div className={`card-body ${className}`}>{children}</div>;
};

Card.Footer = function CardFooter({ children, className = '' }: CardProps) {
  return <div className={`card-footer ${className}`}>{children}</div>;
};

Card.Title = function CardTitle({ children, className = '' }: CardProps) {
  return <h3 className={`card-title ${className}`}>{children}</h3>;
};

Card.Description = function CardDescription({ children, className = '' }: CardProps) {
  return <p className={`card-description ${className}`}>{children}</p>;
};

// Usage
<Card>
  <Card.Header>
    <Card.Title>User Profile</Card.Title>
    <Card.Description>Manage your profile information</Card.Description>
  </Card.Header>
  <Card.Body>
    <UserForm />
  </Card.Body>
  <Card.Footer>
    <Button>Save</Button>
    <Button variant="outline">Cancel</Button>
  </Card.Footer>
</Card>

4. Controlled vs Uncontrolled Pattern

Support both controlled and uncontrolled modes in a single component.

// components/Input.tsx
interface InputProps {
  value?: string;  // Controlled
  defaultValue?: string;  // Uncontrolled
  onChange?: (value: string) => void;
  placeholder?: string;
}

export function Input({
  value: controlledValue,
  defaultValue,
  onChange,
  placeholder,
}: InputProps) {
  // Internal state for uncontrolled mode
  const [internalValue, setInternalValue] = useState(defaultValue ?? '');

  // Determine if controlled
  const isControlled = controlledValue !== undefined;
  const value = isControlled ? controlledValue : internalValue;

  const handleChange = (e: React.ChangeEvent<HTMLInputElement>) => {
    const newValue = e.target.value;

    if (!isControlled) {
      setInternalValue(newValue);
    }

    onChange?.(newValue);
  };

  return (
    <input
      value={value}
      onChange={handleChange}
      placeholder={placeholder}
    />
  );
}

// Usage - Controlled
function ControlledExample() {
  const [value, setValue] = useState('');
  return <Input value={value} onChange={setValue} />;
}

// Usage - Uncontrolled
function UncontrolledExample() {
  return <Input defaultValue="initial" onChange={(val) => console.log(val)} />;
}

5. Provider Pattern

Share data and functions across component tree without prop drilling.

// context/ThemeContext.tsx
interface Theme {
  colors: {
    primary: string;
    secondary: string;
    background: string;
  };
  mode: 'light' | 'dark';
}

interface ThemeContextValue {
  theme: Theme;
  setMode: (mode: 'light' | 'dark') => void;
  toggleMode: () => void;
}

const ThemeContext = createContext<ThemeContextValue | null>(null);

export function useTheme() {
  const context = useContext(ThemeContext);
  if (!context) {
    throw new Error('useTheme must be used within ThemeProvider');
  }
  return context;
}

const lightTheme: Theme = {
  colors: {
    primary: '#007bff',
    secondary: '#6c757d',
    background: '#ffffff',
  },
  mode: 'light',
};

const darkTheme: Theme = {
  colors: {
    primary: '#0d6efd',
    secondary: '#6c757d',
    background: '#212529',
  },
  mode: 'dark',
};

export function ThemeProvider({ children }: { children: ReactNode }) {
  const [mode, setMode] = useState<'light' | 'dark'>('light');

  const theme = mode === 'light' ? lightTheme : darkTheme;

  const toggleMode = () => {
    setMode((prevMode) => (prevMode === 'light' ? 'dark' : 'light'));
  };

  return (
    <ThemeContext.Provider value={{ theme, setMode, toggleMode }}>
      {children}
    </ThemeContext.Provider>
  );
}

// Usage
function App() {
  return (
    <ThemeProvider>
      <Layout />
    </ThemeProvider>
  );
}

function ThemedButton() {
  const { theme, toggleMode } = useTheme();

  return (
    <button
      style={{ backgroundColor: theme.colors.primary }}
      onClick={toggleMode}
    >
      Toggle Theme
    </button>
  );
}

6. HOC Pattern (Legacy, Hooks Preferred)

Higher-Order Components for cross-cutting concerns.

// hocs/withAuth.tsx
interface WithAuthProps {
  isAuthenticated: boolean;
  user: User | null;
}

function withAuth<P extends object>(
  Component: ComponentType<P & WithAuthProps>
) {
  return function WithAuthComponent(props: P) {
    const { isAuthenticated, user } = useAuth();

    if (!isAuthenticated) {
      return <Navigate to="/login" />;
    }

    return <Component {...props} isAuthenticated={isAuthenticated} user={user} />;
  };
}

// Usage
interface DashboardProps extends WithAuthProps {
  title: string;
}

function Dashboard({ title, user }: DashboardProps) {
  return <div>Welcome {user?.name} to {title}</div>;
}

export default withAuth(Dashboard);

// Better: Use hook instead
function Dashboard({ title }: { title: string }) {
  const { user } = useAuth();
  return <div>Welcome {user?.name} to {title}</div>;
}

Pattern Selection Guide

Best Practices

1. Prefer Hooks Over HOCs/Render Props
2. Use TypeScript for type-safe APIs
3. Document Patterns with examples
4. Keep Components Focused on single responsibility
5. Compose Small Components into larger ones
6. Provide Sensible Defaults
7. Make APIs Flexible but not complex

This skill helps you implement modern React component patterns for building flexible, reusable component libraries.