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