/**
 * Executes asynchronous functions sequentially over each item in the array and returns an array of results.
 * @param {X[]} items - The array of items.
 * @param {(item: X, index: number) => Promise<T>} fn - The asynchronous function to execute over each item.
 * @returns {Promise<T[]>} A promise that resolves to an array of results.
 * @template T, X
 */
export declare function chain<T, X>(items: X[], fn: (item: X, index: number) => Promise<T>): Promise<T[]>;
/**
 * Executes asynchronous functions in parallel over each item in the array and returns an array of results.
 * @param {X[]} items - The array of items.
 * @param {(item: X, index: number) => Promise<T>} fn - The asynchronous function to execute over each item.
 * @returns {Promise<T[]>} A promise that resolves to an array of results.
 * @template T, X
 */
export declare function all<T, X>(items: X[], fn: (item: X, index: number) => Promise<T>): Promise<T[]>;