All files / collections / unstable_first_not_nullish_of.ts

// Copyright 2018-2026 the Deno authors. MIT license.
// This module is browser compatible.

/**
 * Applies the given selector to elements in the given array until a value is
 * produced that is neither `null` nor `undefined` and returns that value.
 * Returns `undefined` if no such value is produced.
 *
 * @experimental **UNSTABLE**: New API, yet to be vetted.
 *
 * @typeParam T The type of the elements in the input array.
 * @typeParam O The type of the value produced by the selector function.
 *
 * @param array The array to select a value from.
 * @param selector The function to extract a value from an element.
 *
 * @returns The first non-`null` and non-`undefined` value produced by the
 * selector function, or `undefined` if no such value is produced.
 *
 * @example Basic usage
 * ```ts
 * import { firstNotNullishOf } from "@std/collections/unstable-first-not-nullish-of";
 * import { assertEquals } from "@std/assert";
 *
 * const tables = [
 *   { number: 11, order: null },
 *   { number: 12, order: "Soup" },
 *   { number: 13, order: "Salad" },
 * ];
 *
 * const nextOrder = firstNotNullishOf(tables, (table) => table.order);
 *
 * assertEquals(nextOrder, "Soup");
 * ```
 */
export function firstNotNullishOf<T, O>(
  array: Iterable<T>,
  selector: (item: T, index: number) => O | undefined | null,
): NonNullable<O> | undefined {
  let index = 0;
  for (const current of array) {
    const selected = selector(current, index++);

    if (selected !== null && selected !== undefined) {
      return selected as NonNullable<O>;
    }
  }

  return undefined;
}