ix/src/iterable/findindex.ts

The Interactive Extensions for JavaScript

import { FindOptions } from './findoptions.js';

/**
 * Returns the index of the first element in the array that satisfies the provided testing function.
 * Otherwise, it returns -1, indicating that no element passed the test.
 *
 * @template T The type of the elements in the source sequence.
 * @param {Iterable<T>} source An 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 {number} The index of the first element in the array that passes the test. Otherwise, -1.
 */
export function findIndex<T>(source: Iterable<T>, options: FindOptions<T>): number {
  const { ['thisArg']: thisArg, ['predicate']: predicate } = options;
  let i = 0;

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