ix/src/iterable/includes.ts

The Interactive Extensions for JavaScript

import { comparer } from '../util/comparer.js';

/**
 *  Determines whether an itreable includes a certain value among its entries, returning true or false as appropriate.
 *
 * @template T The type of elements in the source sequence.
 * @param {Iterable<T>} source The source sequence to search for the item.
 * @param {T} valueToFind The value to search for.
 * @param {number} [fromIndex=0] The position in this iterable at which to begin searching for valueToFind.
 * @returns {boolean} Returns true if the value valueToFind is found within the iterable.
 */
export function includes<T>(source: Iterable<T>, searchElement: T, fromIndex = 0): boolean {
  let fromIdx = fromIndex;
  let i = 0;
  if (Math.abs(fromIdx)) {
    fromIdx = 0;
  }
  for (const item of source) {
    if (i++ > fromIdx && comparer(item, searchElement)) {
      return true;
    }
  }
  return false;
}