Frontend Academy · Lesson

TypeScript with React: FC generics hooks

Type React components with generic props, annotate useState and useRef with explicit types, and type custom hooks that return tuples.

Lesson 3 of 413 steps

TypeScript with React: FC generics hooks is a free Frontend Academy lesson on CoddyKit. This is lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Frontend Academy learning path, and your progress syncs across the web and the CoddyKit app. The Frontend Academy course includes 4 lessons in total.

Typing Components

Modern React: type props with an interface and use a plain function. React.FC exists but is no longer recommended (implicit children, no generics support).

// Recommended:
interface ButtonProps {
  label: string;
  onClick: () => void;
  disabled?: boolean;
}

function Button({ label, onClick, disabled }: ButtonProps) {
  return <button onClick={onClick} disabled={disabled}>{label}</button>;
}

Typing children

Use React.ReactNode for any renderable child.

interface CardProps {
  title: string;
  children: React.ReactNode;
}

function Card({ title, children }: CardProps) {
  return (
    <div className="card">
      <h2>{title}</h2>
      {children}
    </div>
  );
}

Typing useState

useState usually infers from the initial value. Provide an explicit type when initial value is null or doesn't represent the full possible type.

const [count, setCount] = useState(0);              // number
const [name, setName] = useState('');                // string

const [user, setUser] = useState<User | null>(null); // explicit
const [items, setItems] = useState<Item[]>([]);      // explicit array type

Typing useRef

Two forms: ref to a DOM element (initialised to null), or a mutable container.

const inputRef = useRef<HTMLInputElement>(null);
const timerRef = useRef<number | null>(null);

useEffect(() => {
  inputRef.current?.focus();
  timerRef.current = window.setInterval(tick, 1000);
  return () => clearInterval(timerRef.current!);
}, []);

Typing Event Handlers

Use React's synthetic event types.

function Form() {
  function onSubmit(e: React.FormEvent<HTMLFormElement>) {
    e.preventDefault();
  }
  function onChange(e: React.ChangeEvent<HTMLInputElement>) {
    setValue(e.target.value);
  }
  function onClick(e: React.MouseEvent<HTMLButtonElement>) {
    /* ... */
  }
  return <form onSubmit={onSubmit}>...</form>;
}

Generic Components

Components can be generic — TypeScript infers the type parameter from the call site.

interface ListProps<T> {
  items: T[];
  renderItem: (item: T) => React.ReactNode;
  keyOf: (item: T) => string | number;
}

function List<T>({ items, renderItem, keyOf }: ListProps<T>) {
  return <ul>{items.map(i => <li key={keyOf(i)}>{renderItem(i)}</li>)}</ul>;
}

<List<User>
  items={users}
  renderItem={u => u.name}
  keyOf={u => u.id}
/>

Typing Custom Hooks

Custom hooks are functions — type them like any other function. Return tuples need explicit annotation to avoid array widening.

function useToggle(initial = false): [boolean, () => void] {
  const [value, setValue] = useState(initial);
  const toggle = () => setValue(v => !v);
  return [value, toggle]; // tuple — annotation makes this stable
}

const [isOpen, toggle] = useToggle();

Typing Context

createContext needs an initial value of the same type as the value you'll provide. Use a non-null assertion or a default object.

interface AuthContextValue {
  user: User | null;
  signIn: (email: string, pw: string) => Promise<void>;
  signOut: () => void;
}

const AuthContext = createContext<AuthContextValue | null>(null);

export function useAuth() {
  const ctx = useContext(AuthContext);
  if (!ctx) throw new Error('useAuth must be inside AuthProvider');
  return ctx;
}

Typing useReducer

Type the state and the action union explicitly.

type State = { count: number };
type Action =
  | { type: 'increment' }
  | { type: 'decrement' }
  | { type: 'set'; value: number };

function reducer(state: State, action: Action): State {
  switch (action.type) {
    case 'increment': return { count: state.count + 1 };
    case 'decrement': return { count: state.count - 1 };
    case 'set':       return { count: action.value };
  }
}

const [state, dispatch] = useReducer(reducer, { count: 0 });

Avoiding React.FC

React.FC has fallen out of favour: it implicitly adds children, doesn't support generic components cleanly, and inhibits some optimisations. Prefer plain function components with typed props.

ComponentPropsWithoutRef Utility

To inherit a native element's props (extending a button or input), use ComponentPropsWithoutRef.

type ButtonProps = React.ComponentPropsWithoutRef<'button'> & {
  variant?: 'primary' | 'secondary';
};

function Button({ variant = 'primary', ...rest }: ButtonProps) {
  return <button className={`btn ${variant}`} {...rest} />;
}

Quick Check

Why is using React.FC generally discouraged in favour of plain typed function components?

Answer it in the interactive lesson

Recap: TypeScript + React

Type props with interfaces, prefer plain functions over React.FC. children: React.ReactNode. useState often infers, annotate for null/empty arrays. useRef for DOM elements. React event types for handlers. Generic components for reusable lists/forms. Tuple return from custom hooks needs annotation. ComponentPropsWithoutRef to extend native elements.

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Frequently Asked Questions

Is the “TypeScript with React: FC generics hooks” lesson free?

Yes — the full text of “TypeScript with React: FC generics hooks” is free to read here on the web. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Frontend Academy course, upgrade to CoddyKit PRO. The Frontend Academy course includes 4 lessons in total.

What will I learn in “TypeScript with React: FC generics hooks”?

Type React components with generic props, annotate useState and useRef with explicit types, and type custom hooks that return tuples. You practise Frontend Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Frontend Academy?

No prior experience is required. Frontend Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 3 of 4.

How long does the “TypeScript with React: FC generics hooks” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

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All lessons in this course

Template Literal Types
Decorators and Metadata
TypeScript with React: FC generics hooks
Strict Mode and Eliminating any

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