JasonDocton React Patterns
React 19+ with TypeScript.
Rules
| Pattern | Do | Don't |
|---|---|---|
| Components | named exports | export default |
| Props | readonly always |
mutable interface |
| Types | explicit function typing | React.FC |
| Defaults | ES6 parameter defaults | defaultProps |
| State | discriminated unions | bag of optionals |
| Errors | Result types (parse/network) | throw for recoverable |
| Critical errors | throw | Result type |
| Effects | render-driven, useEffectEvent |
useEffect with value deps |
React 19 Primitives
| Hook/Component | Purpose |
|---|---|
use() |
extract data from promises |
<Suspense> |
declarative loading states |
useTransition |
loading flags, pending async |
useOptimistic |
instant feedback during mutations |
useDeferredValue |
stable UX during rapid updates |
useEffectEvent |
stable callbacks without re-runs |
useActionState |
workflow-like async state |
<Activity> |
preserve UI state when hidden |
Performance Micro-Patterns
- Derive state during render, not in useEffect
- Hoist static JSX outside component (avoids re-creation)
Component Structure
interface ButtonProps {
readonly variant: "primary" | "secondary"
readonly onClick: () => void
readonly disabled?: boolean
readonly userId: string | undefined // critical fields: explicit
readonly children?: ReactNode
}
export function Button({ variant, onClick, disabled, children }: ButtonProps) {
return <button disabled={disabled}>{children}</button>
}
State with Discriminated Unions
type AsyncState<T> =
| { status: "idle" }
| { status: "loading" }
| { status: "success"; data: T }
| { status: "error"; error: Error }
const [state, setState] = useState<AsyncState<User>>({ status: "idle" })
switch (state.status) {
case "idle": return null
case "loading": return <Spinner />
case "success": return <UserCard user={state.data} />
case "error": return <ErrorMessage error={state.error} />
}
useEffectEvent
// ❌ re-runs on theme change
useEffect(() => {
connection.on("connected", () => showNotification("Connected!", theme));
}, [roomId, theme]);
// ✅ only re-runs on roomId
const => showNotification("Connected!", theme));
useEffect(() => {
connection.on("connected", () => onConnected());
}, [roomId]);
Forms (Actions)
// ✅ useActionState over onSubmit
const [state, formAction, isPending] = useActionState(updateUser, initialState);
Use useFormStatus for pending states in child components.
Result Types
type Result<T, E extends Error> = { ok: true; value: T } | { ok: false; error: E }
const result = parseJson(input)
if (!result.ok) return <Error message={result.error.message} />
Use Result for: parsing, file ops, network. Throw for: validation, critical failures.
Activity Component
<Activity mode={isSearching ? "visible" : "hidden"}>
<SearchSpinner />
</Activity>
Preserves state when hidden — use for tabs, search overlays, conditional UI.
Anti-Patterns
// ❌ React.FC
const Button: React.FC<Props> = () => {};
// ❌ defaultProps
Button.defaultProps = { variant: "primary" };
// ❌ default exports
export default function MyComponent() {}
// ❌ mutable props
interface Props {
count: number;
}