| 1 | import { Observable } from '../Observable';
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| 2 | import { OperatorFunction } from '../types';
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| 3 | /**
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| 4 | * Counts the number of emissions on the source and emits that number when the
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| 5 | * source completes.
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| 6 | *
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| 7 | * <span class="informal">Tells how many values were emitted, when the source
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| 8 | * completes.</span>
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| 9 | *
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| 10 | * 
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| 11 | *
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| 12 | * `count` transforms an Observable that emits values into an Observable that
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| 13 | * emits a single value that represents the number of values emitted by the
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| 14 | * source Observable. If the source Observable terminates with an error, `count`
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| 15 | * will pass this error notification along without emitting a value first. If
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| 16 | * the source Observable does not terminate at all, `count` will neither emit
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| 17 | * a value nor terminate. This operator takes an optional `predicate` function
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| 18 | * as argument, in which case the output emission will represent the number of
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| 19 | * source values that matched `true` with the `predicate`.
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| 20 | *
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| 21 | * ## Examples
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| 22 | *
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| 23 | * Counts how many seconds have passed before the first click happened
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| 24 | * ```ts
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| 25 | * import { fromEvent, interval } from 'rxjs';
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| 26 | * import { count, takeUntil } from 'rxjs/operators';
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| 27 | *
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| 28 | * const seconds = interval(1000);
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| 29 | * const clicks = fromEvent(document, 'click');
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| 30 | * const secondsBeforeClick = seconds.pipe(takeUntil(clicks));
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| 31 | * const result = secondsBeforeClick.pipe(count());
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| 32 | * result.subscribe(x => console.log(x));
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| 33 | * ```
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| 34 | *
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| 35 | * Counts how many odd numbers are there between 1 and 7
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| 36 | * ```ts
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| 37 | * import { range } from 'rxjs';
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| 38 | * import { count } from 'rxjs/operators';
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| 39 | *
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| 40 | * const numbers = range(1, 7);
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| 41 | * const result = numbers.pipe(count(i => i % 2 === 1));
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| 42 | * result.subscribe(x => console.log(x));
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| 43 | * // Results in:
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| 44 | * // 4
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| 45 | * ```
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| 46 | *
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| 47 | * @see {@link max}
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| 48 | * @see {@link min}
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| 49 | * @see {@link reduce}
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| 50 | *
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| 51 | * @param {function(value: T, i: number, source: Observable<T>): boolean} [predicate] A
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| 52 | * boolean function to select what values are to be counted. It is provided with
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| 53 | * arguments of:
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| 54 | * - `value`: the value from the source Observable.
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| 55 | * - `index`: the (zero-based) "index" of the value from the source Observable.
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| 56 | * - `source`: the source Observable instance itself.
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| 57 | * @return {Observable} An Observable of one number that represents the count as
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| 58 | * described above.
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| 59 | * @method count
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| 60 | * @owner Observable
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| 61 | */
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| 62 | export declare function count<T>(predicate?: (value: T, index: number, source: Observable<T>) => boolean): OperatorFunction<T, number>;
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