Switch with never type

Counter.tsx

const reducer = (state: State, action: Actions): State => {
  switch (action.type) {
    case "increment":
      return { count: state.count + action.incrementStep };
    case "decrement":
      return { count: state.count - action.decrementStep };
    default:
      neverReached(action);
  }
};

const neverReached = (never: never) => {};