React TypeScript

Type-safe React = compile-time guarantees = confident refactoring.

<when_to_use>

• Building typed React components
• Implementing generic components
• Typing event handlers, forms, refs
• Using React 19 features (Actions, Server Components, use())
• Router integration (TanStack Router, React Router)
• Custom hooks with proper typing

NOT for: non-React TypeScript, vanilla JS React

</when_to_use>

<react_19_changes>

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.

</react_19_changes>

<component_patterns>

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: