import type { PartialObserver } from './types/inputs/Observer.js';
import type { Subscribable, SubscribableValue } from './types/inputs/Subscribable.js';
import type { MappingKey } from './types/mapping.js';
import type { ListenEventMap, StrictListenable } from './types/outputs/StrictListenable.js';
export type WatchCleanup = () => void;
export type WatchCallback<in D = any> = (data: D) => WatchCleanup | void;
export interface WatchObserver<in D = unknown> extends PartialObserver<D> {
    next?: ((data: D) => void | WatchCleanup) | undefined;
    error?: ((error: unknown) => void | WatchCleanup) | undefined;
}
/**
 * Register a callback that may return a cleanup function.
 * The cleanup function will be called before next call of the callback or when the observable completes.
 */
export declare function watch$<O extends Subscribable>(observable: O, callback: WatchCallback<SubscribableValue<O>>): ReturnType<O['subscribe']>;
/**
 * Register an observer that may return a cleanup function.
 * The cleanup function will be called before next call of the callback or when the observable completes.
 */
export declare function watch$<O extends Subscribable>(observable: O, observer: Partial<WatchObserver<SubscribableValue<O>>>): ReturnType<O['subscribe']>;
/**
 * Register a callback to a given event that may return a cleanup function.
 * The cleanup function will be called before next call of the callback or when the observable completes.
 */
export declare function watch$<L extends StrictListenable, K extends MappingKey<ListenEventMap<L>>>(listenable: L, key: K, observer: WatchCallback<ListenEventMap<L>[K]>): ReturnType<L['on']>;
/**
 * Register an observer to a given event that may return a cleanup function.
 * The cleanup function will be called before next call of the callback or when the observable completes.
 */
export declare function watch$<L extends StrictListenable, K extends MappingKey<ListenEventMap<L>>>(listenable: L, key: K, observer: Partial<WatchObserver<ListenEventMap<L>[K]>>): ReturnType<L['on']>;