/**
 * Transforms chunks from one value to another.
 *
 * @group Transformers
 * @example
 * ```
 * --1----2----3----4----|
 *
 * map((x) => x + 1)
 *
 * --2----3----4----5----|
 * ```
 */
export declare function map<I, O>(fn: (x: I) => O | Promise<O>): TransformStream<I, O>;