button.tsx

interface AsButtonProps {
  as: 'button';
  onClick?: React.EventHandler<React.MouseEvent>;
  formAction?: string;
  // [edited for brevity]
}
    
interface AsAnchorProps {
  as: 'a';
  href: string;
  rel?: string;
  // [edited for brevity]
}
    
export type ButtonProps = AsButtonProps | AsAnchorProps;
    
    
/**
 * If you now start typing `<Button as="" />, your IDE
 * will suggest the 2 possible modes, and when you choose
 * 'a', it will suggest & validate the correct props.
 */