@reactivex/ix-esnext-esm/asynciterable/count.js

The Interactive Extensions for JavaScript

import { wrapWithAbort } from './operators/withabort';
import { throwIfAborted } from '../aborterror';
/**
 * Returns a promise that represents how many elements in the specified async-iterable sequence satisfy a condition
 * otherwise, the number of items in the sequence.
 *
 * @export
 * @template T The type of elements in the source collection.
 * @param {AsyncIterable<T>} source An async-iterable sequence that contains elements to be counted.
 * @param {OptionalFindOptions<T>} [options] The options for a predicate for filtering, thisArg for binding and AbortSignal for cancellation.
 * @returns {Promise<number>} The number of matching elements for the given condition if provided, otherwise
 * the number of elements in the sequence.
 */
export async function count(source, options) {
    const { ['signal']: signal, ['thisArg']: thisArg, ['predicate']: predicate = async () => true } = options || {};
    throwIfAborted(signal);
    let i = 0;
    for await (const item of wrapWithAbort(source, signal)) {
        if (await predicate.call(thisArg, item, i, signal)) {
            i++;
        }
    }
    return i;
}

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