export const hasType = <
  T extends { type: string },
  U extends T['type'],
>(
  value: T,
  type: U,
): value is Extract<T, { type: U }> => value.type === type;

// Usage
type Event =
  | { type: 'click'; x: number; y: number }
  | { type: 'keydown'; key: string };

function handleEvent(event: Event) {
  if (hasType(event, 'click')) {
    console.log(event.x, event.y); // Narrowed to click type
  } else {
    console.log(event.key); // Narrowed to keydown type
  }
}