ix/src/asynciterable/findindex.ts

The Interactive Extensions for JavaScript

import { wrapWithAbort } from './operators/withabort.js';
import { throwIfAborted } from '../aborterror.js';
import { FindOptions } from './findoptions.js';

/**
 * Returns the a Promise containing the index of the first element in the array that satisfies the provided testing function.
 * Otherwise, it returns a Promise with -1, indicating that no element passed the test.
 *
 * @template T The type of the elements in the source sequence.
 * @param {AsyncIterable<T>} source An async-iterable sequence whose elements to apply the predicate to.
 * @param {FindOptions<T>} options The options for a predicate for filtering, thisArg for binding and AbortSignal for cancellation.
 * @returns {Promise<number>} A promise containing the index of the first element in the array that passes the test. Otherwise, -1.
 */
export async function findIndex<T>(
  source: AsyncIterable<T>,
  options: FindOptions<T>
): Promise<number> {
  const { ['signal']: signal, ['thisArg']: thisArg, ['predicate']: predicate } = options;
  throwIfAborted(signal);
  let i = 0;

  for await (const item of wrapWithAbort(source, signal)) {
    if (await predicate.call(thisArg, item, i++, signal)) {
      return i;
    }
  }
  return -1;
}