import 'intersection-observer';
import * as i0 from "@angular/core";
export declare class ViewportService {
    private observer;
    constructor();
    observe(element: any, callback: (inViewport: boolean) => void): void;
    cancel(element: Element): void;
    private triggerViewportChange;
    addViewportChangeListener(element: Element, callback: (inViewport: boolean) => void): void;
    removeViewportChangeListener(element: Element): void;
    static ɵfac: i0.ɵɵFactoryDeclaration<ViewportService, never>;
    static ɵprov: i0.ɵɵInjectableDeclaration<ViewportService>;
}