export declare class ObserverServiceConfig {
    root?: Element | null;
    rootMargin?: string;
    threshold?: number | number[];
}
export declare type CallbackType = (inViewport: boolean) => void;
export interface WatchedItem {
    element: Element;
    callback: CallbackType;
}
export declare class ObserverService {
    options: ObserverServiceConfig;
    supported: boolean;
    watching: Array<WatchedItem>;
    observer: IntersectionObserver | null;
    /**
     * Assigns the user config if they wish to
     * override the defaults by using forRoot
     * @param {ObserverServiceConfig} config
     */
    constructor(config: ObserverServiceConfig);
    /**
     * Handles events made by the observer
     * @param {IntersectionObserverEntry[]} entries
     */
    handleEvent(entries: IntersectionObserverEntry[]): void;
    /**
     * Adds the target to our array so we can call its
     * call back when it enters the viewport
     * @param {Element} el
     * @param {CallbackType} callback
     */
    addTarget(el: Element, callback: CallbackType): void;
    isSupported(): boolean;
}