This skill should be used when building React components with TypeScript, typing hooks, handling events, or when React TypeScript, React 19, Server Components are mentioned...
Type-safe React = compile-time guarantees = confident refactoring.
NOT for: non-React TypeScript, vanilla JS React
React 19 breaking changes require migration. Key patterns:
ref as prop - forwardRef deprecated:
// React 19 - ref as regular prop
type ButtonProps = {
ref?: React.Ref<HTMLButtonElement>;
} & React.ComponentPropsWithoutRef<'button'>;
function Button({ ref, children, ...props }: ButtonProps) {
return <button ref={ref} {...props}>{children}</button>;
}
useActionState - replaces useFormState:
import { useActionState } from 'react';
type FormState = { errors?: string[]; success?: boolean };
function Form() {
const [state, formAction, isPending] = useActionState(submitAction, {});
return <form action={formAction}>...</form>;
}
use() - unwraps promises/context:
function UserProfile({ userPromise }: { userPromise: Promise<User> }) {
const user = use(userPromise); // Suspends until resolved
return <div>{user.name}</div>;
}
See react-19-patterns.md for useOptimistic, useTransition, migration checklist.
Props - extend native elements:
type ButtonProps = {
variant: 'primary' | 'secondary';
} & React.ComponentPropsWithoutRef<'button'>;
function Button({ variant, children, ...props }: ButtonProps) {
return <button className={variant} {...props}>{children}</button>;
}
Children typing:
type Props = {
children: React.ReactNode; // Anything renderable
icon: React.ReactElement; // Single element
render: (data: T) => React.ReactNode; // Render prop
};
Discriminated unions for variant props:
type ButtonProps =
| { variant: 'link'; href: string }
| { variant: 'button'; onClick: () => void };
function Button(props: ButtonProps) {
if (props.variant === 'link') {
return <a href={props.href}>Link</a>;
}
return <button onClick={props.onClick}>Button</button>;
}
Use specific event types for accurate target typing:
// Mouse
function handleClick(e: React.MouseEvent<HTMLButtonElement>) {
e.currentTarget.disabled = true;
}
// Form
function handleSubmit(e: React.FormEvent<HTMLFormElement>) {
e.preventDefault();
const formData = new FormData(e.currentTarget);
}
// Input
function handleChange(e: React.ChangeEvent<HTMLInputElement>) {
console.log(e.target.value);
}
// Keyboard
function handleKeyDown(e: React.KeyboardEvent<HTMLInputElement>) {
if (e.key === 'Enter') e.currentTarget.blur();
}
See event-handlers.md for focus, drag, clipboard, touch, wheel events.
useState - explicit for unions/null:
const [user, setUser] = useState<User | null>(null);
const [status, setStatus] = useState<'idle' | 'loading'>('idle');
useRef - null for DOM, value for mutable:
const inputRef = useRef<HTMLInputElement>(null); // DOM - use ?.
const countRef = useRef<number>(0); // Mutable - direct access
useReducer - discriminated unions for actions:
type Action =
| { type: 'increment' }
| { type: 'set'; payload: number };
function reducer(state: State, action: Action): State {
switch (action.type) {
case 'set': return { ...state, count: action.payload };
default: return state;
}
}
Custom hooks - tuple returns with as const:
function useToggle(initial = false) {
const [value, setValue] = useState(initial);
const toggle = () => setValue(v => !v);
return [value, toggle] as const;
}
useContext - null guard pattern:
const UserContext = createContext<User | null>(null);
function useUser() {
const user = useContext(UserContext);
if (!user) throw new Error('useUser outside UserProvider');
return user;
}
See hooks.md for useCallback, useMemo, useImperativeHandle, useSyncExternalStore.
Generic components infer types from props - no manual annotations at call site.
Pattern - keyof T for column keys, render props for custom rendering:
type Column<T> = {
key: keyof T;
header: string;
render?: (value: T[keyof T], item: T) => React.ReactNode;
};
type TableProps<T> = {
data: T[];
columns: Column<T>[];
keyExtractor: (item: T) => string | number;
};
function Table<T>({ data, columns, keyExtractor }: TableProps<T>) {
return (
<table>
<thead>
<tr>{columns.map(col => <th key={String(col.key)}>{col.header}</th>)}</tr>
</thead>
<tbody>
{data.map(item => (
<tr key={keyExtractor(item)}>
{columns.map(col => (
<td key={String(col.key)}>
{col.render ? col.render(item[col.key], item) : String(item[col.key])}
</td>
))}
</tr>
))}
</tbody>
</table>
);
}
Constrained generics for required properties:
type HasId = { id: string | number };
function List<T extends HasId>({ items }: { items: T[] }) {
return <ul>{items.map(item => <li key={item.id}>...</li>)}</ul>;
}
See generic-components.md for Select, List, Modal, FormField patterns.
React 19 Server Components run on server, can be async.
Async data fetching:
export default async function UserPage({ params }: { params: { id: string } }) {
const user = await fetchUser(params.id);
return <div>{user.name}</div>;
}
Server Actions - 'use server' for mutations:
'use server';
export async function updateUser(userId: string, formData: FormData) {
await db.user.update({ where: { id: userId }, data: { ... } });
revalidatePath(`/users/${userId}`);
}
Client + Server Action:
'use client';
import { useActionState } from 'react';
import { updateUser } from '@/actions/user';
function UserForm({ userId }: { userId: string }) {
const [state, formAction, isPending] = useActionState(
(prev, formData) => updateUser(userId, formData), {}
);
return <form action={formAction}>...</form>;
}
use() for promise handoff:
// Server: pass promise without await
async function Page() {
const userPromise = fetchUser('123');
return <UserProfile userPromise={userPromise} />;
}
// Client: unwrap with use()
'use client';
function UserProfile({ userPromise }: { userPromise: Promise<User> }) {
const user = use(userPromise);
return <div>{user.name}</div>;
}
See server-components.md for parallel fetching, streaming, error boundaries.
Both TanStack Router and React Router v7 provide type-safe routing solutions.
TanStack Router - Compile-time type safety with Zod validation:
import { createRoute } from '@tanstack/react-router';
import { z } from 'zod';
const userRoute = createRoute({
path: '/users/$userId',
component: UserPage,
loader: async ({ params }) => ({ user: await fetchUser(params.userId) }),
validateSearch: z.object({
tab: z.enum(['profile', 'settings']).optional(),
page: z.number().int().positive().default(1),
}),
});
function UserPage() {
const { user } = useLoaderData({ from: userRoute.id });
const { tab, page } = useSearch({ from: userRoute.id });
const { userId } = useParams({ from: userRoute.id });
}
React Router v7 - Automatic type generation with Framework Mode:
import type { Route } from "./+types/user";
export async function loader({ params }: Route.LoaderArgs) {
return { user: await fetchUser(params.userId) };
}
export default function UserPage({ loaderData }: Route.ComponentProps) {
const { user } = loaderData; // Typed from loader
return <h1>{user.name}</h1>;
}
See tanstack-router.md for TanStack patterns and react-router.md for React Router patterns.
ALWAYS:
NEVER:
