excatt/composition-patterns

React Composition Patterns

Composition patterns for flexible and maintainable React components. Avoid boolean prop abuse, use compound components, state lifting, and composing internals.

Rule Categories (by Priority)

| Priority | Category | Impact | Description | |:--------:|----------|:------:|-------------| | 1 | Component Architecture | HIGH | Component structuring | | 2 | State Management | MEDIUM | State management patterns | | 3 | Implementation Patterns | MEDIUM | Implementation patterns | | 4 | React 19 APIs | MEDIUM | React 19 changes |

---

1. Component Architecture (HIGH)

1.1 Prevent Boolean Prop Abuse

Impact: CRITICAL

Boolean props lead to combinatorial explosion. Use composition instead.

// ❌ Boolean prop explosion - unmaintainable
function Composer({
  isThread,
  isDMThread,
  isEditing,
  isForwarding,
}: Props) {
  return (
    <form>
      {isDMThread ? <DMField /> : isThread ? <ThreadField /> : null}
      {isEditing ? <EditActions /> : isForwarding ? <ForwardActions /> : <DefaultActions />}
    </form>
  )
}

// ✅ Composition - explicit variants
function ThreadComposer({ channelId }: { channelId: string }) {
  return (
    <Composer.Frame>
      <Composer.Input />
      <AlsoSendToChannelField id={channelId} />
      <Composer.Footer>
        <Composer.Submit />
      </Composer.Footer>
    </Composer.Frame>
  )
}

function EditComposer() {
  return (
    <Composer.Frame>
      <Composer.Input />
      <Composer.Footer>
        <Composer.CancelEdit />
        <Composer.SaveEdit />
      </Composer.Footer>
    </Composer.Frame>
  )
}

1.2 Use Compound Components

Impact: HIGH

Structure complex components into subcomponents connected by shared context.

// ❌ Monolithic + render props
function Composer({
  renderHeader,
  renderFooter,
  showAttachments,
}: Props) {
  return (
    <form>
      {renderHeader?.()}
      <Input />
      {showAttachments && <Attachments />}
      {renderFooter?.()}
    </form>
  )
}

// ✅ Compound components + shared context
const ComposerContext = createContext<ComposerContextValue | null>(null)

function ComposerProvider({ children, state, actions, meta }: ProviderProps) {
  return (
    <ComposerContext value={{ state, actions, meta }}>
      {children}
    </ComposerContext>
  )
}

function ComposerInput() {
  const { state, actions: { update } } = use(ComposerContext)
  return <TextInput value={state.input} onChangeText={text => update(s => ({ ...s, input: text }))} />
}

// Export as compound component
const Composer = {
  Provider: ComposerProvider,
  Frame: ComposerFrame,
  Input: ComposerInput,
  Submit: ComposerSubmit,
  Footer: ComposerFooter,
}

// Usage
<Composer.Provider state={state} actions={actions} meta={meta}>
  <Composer.Frame>
    <Composer.Input />
    <Composer.Footer>
      <Composer.Submit />
    </Composer.Footer>
  </Composer.Frame>
</Composer.Provider>

---

2. State Management (MEDIUM)

2.1 Separate State Implementation from UI

Impact: MEDIUM

Provider knows state implementation, UI only uses context interface.

// ❌ UI coupled to state implementation
function ChannelComposer({ channelId }: { channelId: string }) {
  const state = useGlobalChannelState(channelId)  // Coupled to specific implementation
  const { submit } = useChannelSync(channelId)
  return <Composer.Input value={state.input} />
}

// ✅ State management separated in Provider
function ChannelProvider({ channelId, children }: Props) {
  const { state, update, submit } = useGlobalChannel(channelId)
  return (
    <Composer.Provider state={state} actions={{ update, submit }}>
      {children}
    </Composer.Provider>
  )
}

// UI only needs interface
function ChannelComposer() {
  return (
    <Composer.Frame>
      <Composer.Input />  {/* Reads state from context */}
      <Composer.Submit />
    </Composer.Frame>
  )
}

2.2 Define Generic Context Interface

Impact: HIGH

Define generic interface with 3 parts: state, actions, meta.

// Generic interface - any provider can implement
interface ComposerContextValue {
  state: {
    input: string
    attachments: Attachment[]
    isSubmitting: boolean
  }
  actions: {
    update: (updater: (state: State) => State) => void
    submit: () => void
  }
  meta: {
    inputRef: React.RefObject<TextInput>
  }
}

// Provider A: Local state
function ForwardMessageProvider({ children }) {
  const [state, setState] = useState(initialState)
  return <ComposerContext value={{ state, actions: { update: setState, submit }, meta }}>{children}</ComposerContext>
}

// Provider B: Global synced state
function ChannelProvider({ channelId, children }) {
  const { state, update, submit } = useGlobalChannel(channelId)
  return <ComposerContext value={{ state, actions: { update, submit }, meta }}>{children}</ComposerContext>
}

// Same UI works with both providers!

2.3 Lift State to Provider

Impact: HIGH

Lift state to Provider so sibling components can access it.

// ❌ State trapped inside component
function ForwardMessageDialog() {
  return (
    <Dialog>
      <ForwardMessageComposer />  {/* state trapped here */}
      <MessagePreview />          {/* Cannot access state! */}
      <ForwardButton />           {/* Cannot call submit! */}
    </Dialog>
  )
}

// ✅ Lift state to Provider
function ForwardMessageDialog() {
  return (
    <ForwardMessageProvider>
      <Dialog>
        <ForwardMessageComposer />
        <MessagePreview />    {/* Access state via context */}
        <ForwardButton />     {/* Call submit via context */}
      </Dialog>
    </ForwardMessageProvider>
  )
}

// Anywhere inside Provider can access state/actions
function ForwardButton() {
  const { actions } = use(ComposerContext)
  return <Button onPress={actions.submit}>Forward</Button>
}

---

3. Implementation Patterns (MEDIUM)

3.1 Create Explicit Component Variants

Impact: MEDIUM

Create explicit variant components instead of boolean props.

// ❌ Unclear what UI renders
<Composer isThread isEditing={false} channelId="abc" showAttachments />

// ✅ Immediately clear
<ThreadComposer channelId="abc" />
<EditMessageComposer messageId="xyz" />
<ForwardMessageComposer messageId="123" />

3.2 Prefer Children over Render Props

Impact: MEDIUM

Use children for composition instead of renderX props.

// ❌ Render props - hard to read
<Composer
  renderHeader={() => <CustomHeader />}
  renderFooter={() => <><Formatting /><Emojis /></>}
/>

// ✅ Children - natural composition
<Composer.Frame>
  <CustomHeader />
  <Composer.Input />
  <Composer.Footer>
    <Composer.Formatting />
    <Composer.Emojis />
  </Composer.Footer>
</Composer.Frame>

When render props appropriate: Parent needs to pass data to children

<List data={items} renderItem={({ item, index }) => <Item item={item} />} />

---

4. React 19 APIs (MEDIUM)

⚠️ React 19+ only. Skip this section for React 18 or below.

4.1 React 19 API Changes

// ❌ forwardRef (unnecessary in React 19)
const ComposerInput = forwardRef<TextInput, Props>((props, ref) => {
  return <TextInput ref={ref} {...props} />
})

// ✅ ref as regular prop
function ComposerInput({ ref, ...props }: Props & { ref?: React.Ref<TextInput> }) {
  return <TextInput ref={ref} {...props} />
}

// ❌ useContext (React 19)
const value = useContext(MyContext)

// ✅ use() - conditional calls possible
const value = use(MyContext)

---

Quick Checklist

| Check | Rule | |:----:|------| | [ ] | 3+ Boolean props? → Refactor to composition | | [ ] | Complex conditional rendering? → Create explicit variants | | [ ] | State trapped in component? → Lift to Provider | | [ ] | renderX props? → Change to children | | [ ] | React 19? → Remove forwardRef, use use() |

Related Skills

• /react-best-practices - Performance optimization (waterfall, bundle, rendering)
• /web-design-guidelines - UI/UX quality (accessibility, interaction)
• /design-patterns - General design patterns