import type { Observer } from '../inputs/Observer.js';
import type { Subscription } from './Subscription.js';
/**
 * Object receiving data from an observable.
 *
 * @since 2.0.0
 * @see Observer
 * @see observer$
 */
export interface StrictObserver<in D = unknown> extends Observer<D> {
    /**
     * Called at the start of a subscription with the generated subscription object
     * @param subscription
     *
     * @since 2.0.0
     */
    start?(this: void, subscription: Subscription): void;
    /**
     * Called with each emitted value
     * @param data
     *
     * @since 2.0.0
     */
    next(this: void, data: D): void;
    /**
     * Called when an error occurs in the observable
     * @param err
     *
     * @since 2.0.0
     */
    error(this: void, err: unknown): void;
    /**
     * Called when the observable completes. No other data or error will then be received.
     *
     * @since 2.0.0
     */
    complete(this: void): void;
}