SKILL.md
$27
Instructions
- Apply these patterns during component design, code generation, and review. When you see boolean prop accumulation or rigid component APIs, suggest the appropriate composition pattern.
Details
Overview
The core principle: composition over configuration. Instead of adding boolean props and conditional branches to handle every variant, compose smaller, focused components together. This makes components easier to understand, test, and extend — for both humans and AI agents.
1. Replace Boolean Props with Composition
Impact: HIGH — Prevents combinatorial explosion and makes intent explicit.
Boolean props multiply complexity: 4 booleans = 16 possible states, most of which are untested. Replace them with composable children.
Avoid — boolean prop accumulation:
<Card
showHeader
showFooter
collapsible
bordered
withShadow
headerAction="close"
size="large"
/>Prefer — explicit composition:
<Card variant="bordered" shadow="md">
<Card.Header>
<h3>Title</h3>
<Card.CloseButton />
</Card.Header>
<Card.Body collapsible>
<p>Content here</p>
</Card.Body>
<Card.Footer>
<Button>Save</Button>
</Card.Footer>
</Card>Each piece is explicit, testable, and independently optional.
2. Build Compound Components with Context
Impact: HIGH — Shared implicit state without prop drilling.
Compound components are a group of components that work together, sharing state through context rather than props. The parent owns the state; children consume it.
Avoid — parent manages everything through props:
<Select
options={options}
value={value}
onChange={onChange}
renderOption={(opt) => <span>{opt.icon} {opt.label}</span>}
renderSelected={(opt) => <b>{opt.label}</b>}
placeholder="Choose..."
clearable
searchable
maxHeight={300}
/>Prefer — compound components:
const SelectContext = createContext<SelectState | null>(null)
function Select({ children, value, onChange }: SelectProps) {
const [open, setOpen] = useState(false)
const ctx = useMemo(() => ({ value, onChange, open, setOpen }), [value, onChange, open])
return (
<SelectContext.Provider value={ctx}>
<div className="select-root">{children}</div>
</SelectContext.Provider>
)
}
function Trigger({ children }: { children: React.ReactNode }) {
const { open, setOpen } = useSelectContext()
return <button onClick={() => setOpen(!open)}>{children}</button>
}
function Options({ children }: { children: React.ReactNode }) {
const { open } = useSelectContext()
if (!open) return null
return <ul role="listbox">{children}</ul>
}
function Option({ value, children }: OptionProps) {
const { value: selected, onChange, setOpen } = useSelectContext()
return (
<li
role="option"
aria-selected={value === selected}
onClick={() => { onChange(value); setOpen(false) }}
>
{children}
</li>
)
}
Select.Trigger = Trigger
Select.Options = Options
Select.Option = OptionUsage:
<Select value={color} onChange={setColor}>
<Select.Trigger>Pick a color</Select.Trigger>
<Select.Options>
<Select.Option value="red">Red</Select.Option>
<Select.Option value="blue">Blue</Select.Option>
</Select.Options>
</Select>3. Create Explicit Variant Components
Impact: MEDIUM — Makes each mode a clear, focused component.
When a component has distinct "modes" (dialog vs drawer, inline vs modal, card vs list-item), create explicit variant components instead of toggling with props.
Avoid — one component with mode props:
function MediaDisplay({ type, src, title, showControls, autoPlay, loop }: Props) {
if (type === 'video') {
return <video src={src} controls={showControls} autoPlay={autoPlay} loop={loop} />
}
if (type === 'audio') {
return <audio src={src} controls={showControls} />
}
return <img src={src} alt={title} />
}Prefer — explicit variants:
function VideoPlayer({ src, controls, autoPlay, loop }: VideoProps) {
return <video src={src} controls={controls} autoPlay={autoPlay} loop={loop} />
}
function AudioPlayer({ src, controls }: AudioProps) {
return <audio src={src} controls={controls} />
}
function Image({ src, alt }: ImageProps) {
return <img src={src} alt={alt} />
}Each variant has exactly the props it needs — no impossible states, no unused props.
4. Use Children Over Render Props for Composition
Impact: MEDIUM — Simpler API, better readability.
Render props (renderHeader, renderItem) were essential before hooks, but today children provides cleaner composition for most cases.
Avoid — render prop proliferation:
<DataTable
data={users}
renderHeader={() => <h2>Users</h2>}
renderRow={(user) => <UserRow user={user} />}
renderEmpty={() => <EmptyState />}
renderFooter={() => <Pagination />}
/>Prefer — children composition:
<DataTable data={users}>
<DataTable.Header>
<h2>Users</h2>
</DataTable.Header>
<DataTable.Body>
{users.map(user => <UserRow key={user.id} user={user} />)}
</DataTable.Body>
<DataTable.Empty>
<EmptyState />
</DataTable.Empty>
<DataTable.Footer>
<Pagination />
</DataTable.Footer>
</DataTable>Reserve render props for cases where the parent needs to provide data to the renderer (e.g., virtualized list items).
5. Decouple State Implementation from UI
Impact: MEDIUM — Swap state management without changing components.
Define a generic interface for your state shape (value, actions, metadata), then let providers implement it. Components consume the interface, not the implementation.
Define the interface:
interface CounterState {
count: number
increment: () => void
decrement: () => void
isLoading: boolean
}
const CounterContext = createContext<CounterState | null>(null)
function useCounter() {
const ctx = useContext(CounterContext)
if (!ctx) throw new Error('useCounter must be used within a CounterProvider')
return ctx
}Implement with local state:
function LocalCounterProvider({ children }: { children: React.ReactNode }) {
const [count, setCount] = useState(0)
const value = useMemo(() => ({
count,
increment: () => setCount(c => c + 1),
decrement: () => setCount(c => c - 1),
isLoading: false,
}), [count])
return <CounterContext.Provider value={value}>{children}</CounterContext.Provider>
}Swap to API-backed state without changing consumers:
function ApiCounterProvider({ children }: { children: React.ReactNode }) {
const { data, mutate } = useSWR('/api/counter', fetcher)
const value = useMemo(() => ({
count: data?.count ?? 0,
increment: () => mutate(patch('/api/counter', { delta: 1 })),
decrement: () => mutate(patch('/api/counter', { delta: -1 })),
isLoading: !data,
}), [data, mutate])
return <CounterContext.Provider value={value}>{children}</CounterContext.Provider>
}The useCounter() consumers never change.
6. Lift State to Provider Components
Impact: MEDIUM — Enables sibling communication without prop threading.
When two sibling components need shared state, lift it into a provider rather than threading callbacks through the parent.
Avoid — parent threads state to siblings:
function Page() {
const [selected, setSelected] = useState<string | null>(null)
return (
<div>
<Sidebar selected={selected} onSelect={setSelected} />
<Detail selected={selected} />
</div>
)
}Prefer — provider manages shared state:
function SelectionProvider({ children }: { children: React.ReactNode }) {
const [selected, setSelected] = useState<string | null>(null)
return (
<SelectionContext.Provider value={{ selected, setSelected }}>
{children}
</SelectionContext.Provider>
)
}
function Page() {
return (
<SelectionProvider>
<Sidebar />
<Detail />
</SelectionProvider>
)
}Both Sidebar and Detail consume useSelection() directly.
7. Use Polymorphic as Props for Flexible Elements
Impact: MEDIUM — One component, any underlying element or component.
The as prop pattern lets consumers control the rendered element while keeping your component's styles and behavior.
type BoxProps<C extends React.ElementType = 'div'> = {
as?: C
children: React.ReactNode
} & Omit<React.ComponentPropsWithoutRef<C>, 'as' | 'children'>
function Box<C extends React.ElementType = 'div'>({
as,
children,
...props
}: BoxProps<C>) {
const Component = as || 'div'
return <Component {...props}>{children}</Component>
}Usage:
<Box>Default div</Box>
<Box as="section">A section</Box>
<Box as="a" href="/about">A link</Box>
<Box as={Link} to="/about">Router link</Box>8. React 19: Drop forwardRef , Use ref as a Prop
Impact: MEDIUM — Simpler component definitions.
React 19 passes ref as a regular prop. No more forwardRef wrapper.
React 18 (deprecated pattern):
const Input = forwardRef<HTMLInputElement, InputProps>(function Input(props, ref) {
return <input ref={ref} {...props} />
})React 19:
function Input({ ref, ...props }: InputProps & { ref?: React.Ref<HTMLInputElement> }) {
return <input ref={ref} {...props} />
}Similarly, use() can read either promises or context and can be called conditionally:
import { use } from 'react'
function Panel({ themePromise }: { themePromise: Promise<Theme> }) {
const theme = use(themePromise) // unwraps promise
const user = use(UserContext) // conditional context read
return <div className={theme.bg}>{user.name}</div>
}9. Slot Pattern for Layout Components
Impact: MEDIUM — Named insertion points without render props.
For layout components with multiple content areas, use a slot pattern based on child type detection or named sub-components.
function AppLayout({ children }: { children: React.ReactNode }) {
const slots = React.Children.toArray(children)
const header = slots.find(
(child): child is React.ReactElement => React.isValidElement(child) && child.type === AppLayout.Header
)
const content = slots.filter(
(child) => !React.isValidElement(child) || child.type !== AppLayout.Header
)
return (
<div className="app-layout">
<header>{header}</header>
<main>{content}</main>
</div>
)
}
AppLayout.Header = function Header({ children }: { children: React.ReactNode }) {
return <>{children}</>
}Usage:
<AppLayout>
<AppLayout.Header>
<Logo />
<Nav />
</AppLayout.Header>
<Dashboard />
</AppLayout>10. Headless Components for Maximum Flexibility
Impact: HIGH — Logic without opinions about rendering.
Headless components provide behavior (state, keyboard handling, ARIA attributes) without any markup. Consumers supply the rendering.
function useToggle(initial = false) {
const [on, setOn] = useState(initial)
const toggle = useCallback(() => setOn(o => !o), [])
const buttonProps = {
'aria-pressed': on,
onClick: toggle,
role: 'switch' as const,
}
return { on, toggle, buttonProps }
}Usage — consumer controls all rendering:
function DarkModeSwitch() {
const { on, buttonProps } = useToggle(false)
return (
<button {...buttonProps} className={on ? 'dark' : 'light'}>
{on ? 'Dark' : 'Light'} Mode
</button>
)
}Libraries like Radix UI, Headless UI, and React Aria follow this pattern. Prefer them over fully-styled component libraries when you need design flexibility.
Source
Patterns from patterns.dev — composition guidance for the broader React community.