import { innerFrom } from '../observable/innerFrom';
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import { MonoTypeOperatorFunction, ObservableInput } from '../types';
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import { operate } from '../util/lift';
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import { noop } from '../util/noop';
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import { createOperatorSubscriber } from './OperatorSubscriber';
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/**
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* Emits the most recently emitted value from the source Observable whenever
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* another Observable, the `notifier`, emits.
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*
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* <span class="informal">It's like {@link sampleTime}, but samples whenever
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* the `notifier` `ObservableInput` emits something.</span>
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*
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* 
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*
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* Whenever the `notifier` `ObservableInput` emits a value, `sample`
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* looks at the source Observable and emits whichever value it has most recently
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* emitted since the previous sampling, unless the source has not emitted
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* anything since the previous sampling. The `notifier` is subscribed to as soon
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* as the output Observable is subscribed.
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*
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* ## Example
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*
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* On every click, sample the most recent `seconds` timer
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*
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* ```ts
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* import { fromEvent, interval, sample } from 'rxjs';
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*
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* const seconds = interval(1000);
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* const clicks = fromEvent(document, 'click');
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* const result = seconds.pipe(sample(clicks));
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*
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* result.subscribe(x => console.log(x));
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* ```
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*
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* @see {@link audit}
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* @see {@link debounce}
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* @see {@link sampleTime}
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* @see {@link throttle}
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*
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* @param notifier The `ObservableInput` to use for sampling the
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* source Observable.
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* @return A function that returns an Observable that emits the results of
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* sampling the values emitted by the source Observable whenever the notifier
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* Observable emits value or completes.
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*/
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export function sample<T>(notifier: ObservableInput<any>): MonoTypeOperatorFunction<T> {
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return operate((source, subscriber) => {
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let hasValue = false;
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let lastValue: T | null = null;
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source.subscribe(
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createOperatorSubscriber(subscriber, (value) => {
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hasValue = true;
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lastValue = value;
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})
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);
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innerFrom(notifier).subscribe(
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createOperatorSubscriber(
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subscriber,
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() => {
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if (hasValue) {
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hasValue = false;
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const value = lastValue!;
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lastValue = null;
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subscriber.next(value);
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}
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},
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noop
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)
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);
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});
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}
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