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

The Interactive Extensions for JavaScript

import { wrapWithAbort } from './operators/withabort.js';
import { throwIfAborted } from '../aborterror.js';
/**
 * Returns the first element of an async-iterable sequence that matches the predicate if provided, or undefined if no such element exists.
 *
 * @template T The type of the elements in the source sequence.
 * @param {AsyncIterable<T>} source Source async-enumerable sequence.
 * @returns {(Promise<S | undefined>)} A Promise containing the first element in the async-iterable sequence,
 * or a default value if no such element exists.
 */
export async function first(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)) {
            return item;
        }
    }
    return undefined;
}

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