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keksAccountGUI/node_modulesOLD/rxjs/internal/operators/count.d.ts

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2019-08-11 18:48:02 +00:00
import { Observable } from '../Observable';
import { OperatorFunction } from '../types';
/**
* Counts the number of emissions on the source and emits that number when the
* source completes.
*
* <span class="informal">Tells how many values were emitted, when the source
* completes.</span>
*
* ![](count.png)
*
* `count` transforms an Observable that emits values into an Observable that
* emits a single value that represents the number of values emitted by the
* source Observable. If the source Observable terminates with an error, `count`
* will pass this error notification along without emitting a value first. If
* the source Observable does not terminate at all, `count` will neither emit
* a value nor terminate. This operator takes an optional `predicate` function
* as argument, in which case the output emission will represent the number of
* source values that matched `true` with the `predicate`.
*
* ## Examples
*
* Counts how many seconds have passed before the first click happened
* ```ts
* import { fromEvent, interval } from 'rxjs';
* import { count, takeUntil } from 'rxjs/operators';
*
* const seconds = interval(1000);
* const clicks = fromEvent(document, 'click');
* const secondsBeforeClick = seconds.pipe(takeUntil(clicks));
* const result = secondsBeforeClick.pipe(count());
* result.subscribe(x => console.log(x));
* ```
*
* Counts how many odd numbers are there between 1 and 7
* ```ts
* import { range } from 'rxjs';
* import { count } from 'rxjs/operators';
*
* const numbers = range(1, 7);
* const result = numbers.pipe(count(i => i % 2 === 1));
* result.subscribe(x => console.log(x));
* // Results in:
* // 4
* ```
*
* @see {@link max}
* @see {@link min}
* @see {@link reduce}
*
* @param {function(value: T, i: number, source: Observable<T>): boolean} [predicate] A
* boolean function to select what values are to be counted. It is provided with
* arguments of:
* - `value`: the value from the source Observable.
* - `index`: the (zero-based) "index" of the value from the source Observable.
* - `source`: the source Observable instance itself.
* @return {Observable} An Observable of one number that represents the count as
* described above.
* @method count
* @owner Observable
*/
export declare function count<T>(predicate?: (value: T, index: number, source: Observable<T>) => boolean): OperatorFunction<T, number>;