drop_last_while.ts

// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
// This module is browser compatible.

/**
 * Returns a new array that drops all elements in the given collection until the
 * last element that does not match the given predicate.
 *
 * @example
 * ```ts
 * import { dropLastWhile } from "https://deno.land/std@$STD_VERSION/collections/drop_last_while.ts";
 * import { assertEquals } from "https://deno.land/std@$STD_VERSION/assert/assert_equals.ts";
 *
 * const numbers = [22, 30, 44];
 *
 * const notFortyFour = dropLastWhile(numbers, (i) => i !== 44);
 *
 * assertEquals(
 *   notFortyFour,
 *   [22, 30],
 * );
 * ```
 */
export function dropLastWhile<T>(
  array: readonly T[],
  predicate: (el: T) => boolean,
): T[] {
  let offset = array.length;
  while (0 < offset && predicate(array[offset - 1] as T)) offset--;

  return array.slice(0, offset);
}