export interface iBlockNav {
    setMessage: (id: string, message?: string) => void;
    onNav: (nav: () => void) => void;
    navPrompt?: JSX.Element;
}
/** set block message if you want to block nav.
 * - call setMessage to  add a blocker message
 * - call onNav when you have internal navigation (open / close popups)
 * - render the navPrompt control to your page
 * FYI for page unload, most modern browsers won't show your message but a generic one instead. */
export declare function useBlockNav(): iBlockNav;