React TypeScript

// add type before parens
React.useState<boolean>(false);
React.useRef<HTMLDivElement>(null);
React.useCallback(
  function () {
    if (theMoon) {
      setSomethingAwesome();
    }
  },
  [theMoon]
);

type FooProps = {
  children: React.ReactNode;
};

// functional
const Foo: React.FC<FooProps> = (props) => ()
// class
class Foo extends React.Component<FooProps> {}

const Foo = styled<FooProps>.div``;