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import { Observable } from '../Observable';
import { MonoTypeOperatorFunction } from '../interfaces';
/**
* Delays the emission of items from the source Observable by a given time span
* determined by the emissions of another Observable.
*
* <span class="informal">It's like {@link delay}, but the time span of the
* delay duration is determined by a second Observable.</span>
*
* <img src="./img/delayWhen.png" width="100%">
*
* `delayWhen` time shifts each emitted value from the source Observable by a
* time span determined by another Observable. When the source emits a value,
* the `delayDurationSelector` function is called with the source value as
* argument, and should return an Observable, called the "duration" Observable.
* The source value is emitted on the output Observable only when the duration
* Observable emits a value or completes.
*
* Optionally, `delayWhen` takes a second argument, `subscriptionDelay`, which
* is an Observable. When `subscriptionDelay` emits its first value or
* completes, the source Observable is subscribed to and starts behaving like
* described in the previous paragraph. If `subscriptionDelay` is not provided,
* `delayWhen` will subscribe to the source Observable as soon as the output
* Observable is subscribed.
*
* @example <caption>Delay each click by a random amount of time, between 0 and 5 seconds</caption>
* var clicks = Rx.Observable.fromEvent(document, 'click');
* var delayedClicks = clicks.delayWhen(event =>
* Rx.Observable.interval(Math.random() * 5000)
* );
* delayedClicks.subscribe(x => console.log(x));
*
* @see {@link debounce}
* @see {@link delay}
*
* @param {function(value: T): Observable} delayDurationSelector A function that
* returns an Observable for each value emitted by the source Observable, which
* is then used to delay the emission of that item on the output Observable
* until the Observable returned from this function emits a value.
* @param {Observable} subscriptionDelay An Observable that triggers the
* subscription to the source Observable once it emits any value.
* @return {Observable} An Observable that delays the emissions of the source
* Observable by an amount of time specified by the Observable returned by
* `delayDurationSelector`.
* @method delayWhen
* @owner Observable
*/
export declare function delayWhen<T>(delayDurationSelector: (value: T) => Observable<any>, subscriptionDelay?: Observable<any>): MonoTypeOperatorFunction<T>;