React Component Architecture

Component Design Principles

1. Single Responsibility - Each component does one thing well
2. Composition Over Configuration - Use children and render props over prop drilling
3. Colocation - Keep related code together (styles, tests, types)
4. Controlled vs Uncontrolled - Be explicit about state ownership

Component Patterns

Compound Components

For complex UI with shared state:

const Tabs = ({ children, defaultValue }: TabsProps) => {
  const [active, setActive] = useState(defaultValue);
  return (
    <TabsContext.Provider value={{ active, setActive }}>
      {children}
    </TabsContext.Provider>
  );
};

Tabs.List = TabsList;
Tabs.Trigger = TabsTrigger;
Tabs.Content = TabsContent;

Render Props for Flexibility

When consumers need control over rendering:

interface ListProps<T> {
  items: T[];
  renderItem: (item: T, index: number) => ReactNode;
  keyExtractor: (item: T) => string;
}

function List<T>({ items, renderItem, keyExtractor }: ListProps<T>) {
  return items.map((item, i) => (
    <Fragment key={keyExtractor(item)}>{renderItem(item, i)}</Fragment>
  ));
}

Custom Hooks for Logic Extraction

Extract reusable stateful logic:

function useToggle(initial = false) {
  const [state, setState] = useState(initial);
  const toggle = useCallback(() => setState(s => !s), []);
  const setTrue = useCallback(() => setState(true), []);
  const setFalse = useCallback(() => setState(false), []);
  return { state, toggle, setTrue, setFalse } as const;
}

Polymorphic Components

Components that render as different elements:

type PolymorphicProps<E extends ElementType> = {
  as?: E;
} & ComponentPropsWithoutRef<E>;

function Box<E extends ElementType = 'div'>({
  as,
  ...props
}: PolymorphicProps<E>) {
  const Component = as || 'div';
  return <Component {...props} />;
}

Props Patterns

Discriminated Union Props

For mutually exclusive prop combinations:

type ButtonProps =
  | { variant: 'link'; href: string; onClick?: never }
  | { variant: 'button'; onClick: () => void; href?: never };

Default Props with Destructuring

function Button({
  variant = 'primary',
  size = 'md',
  ...props
}: ButtonProps) {
  // ...
}

Performance Patterns

1. Memoize expensive computations with useMemo
2. Memoize callbacks passed to children with useCallback
3. Split contexts by update frequency
4. Use React.memo for pure presentational components
5. Virtualize long lists with react-virtual or similar

File Structure

components/
  Button/
    Button.tsx        # Component
    Button.test.tsx   # Tests
    Button.types.ts   # Types (if complex)
    index.ts          # Re-export