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

The Interactive Extensions for JavaScript

import { wrapWithAbort } from './operators/withabort.js';
import { throwIfAborted } from '../aborterror.js';
/**
 * Returns the only element of an async-iterable sequence that matches the predicate if specified,
 * or undefined if no such element exists; this method reports an exception if there is more
 * than one element in the async-iterable sequence.
 *
 * @template T The type of the elements in the source sequence.
 * @param {AsyncIterable<T>} source Source async-iterable sequence.
 * @param {OptionalFindOptions<T>} [options] The optional options which includes a predicate for filtering,
 * thisArg for predicate binding and an abort signal for cancellation.
 * @returns {(Promise<T | undefined>)} A promise with the single element in the async-iterable sequence that satisfies
 * the condition in the predicate, or undefined if no such element exists.
 */
export async function single(source, options) {
    const { ['signal']: signal, ['thisArg']: thisArg, ['predicate']: predicate = async () => true } = options || {};
    throwIfAborted(signal);
    let result;
    let hasResult = false;
    let i = 0;
    for await (const item of wrapWithAbort(source, signal)) {
        if (hasResult && (await predicate.call(thisArg, item, i++, signal))) {
            throw new Error('More than one element was found');
        }
        if (await predicate.call(thisArg, item, i++, signal)) {
            result = item;
            hasResult = true;
        }
    }
    return result;
}

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