/**
 * @license
 * Copyright (c) 2017 The Polymer Project Authors. All rights reserved.
 * This code may only be used under the BSD style license found at
 * http://polymer.github.io/LICENSE.txt
 * The complete set of authors may be found at
 * http://polymer.github.io/AUTHORS.txt
 * The complete set of contributors may be found at
 * http://polymer.github.io/CONTRIBUTORS.txt
 * Code distributed by Google as part of the polymer project is also
 * subject to an additional IP rights grant found at
 * http://polymer.github.io/PATENTS.txt
 */
import { Part } from '../lit-html.js';
/**
 * A directive that renders the items of an async iterable[1], appending new
 * values after previous values, similar to the built-in support for iterables.
 *
 * Async iterables are objects with a [Symbol.asyncIterator] method, which
 * returns an iterator who's `next()` method returns a Promise. When a new
 * value is available, the Promise resolves and the value is appended to the
 * Part controlled by the directive. If another value other than this
 * directive has been set on the Part, the iterable will no longer be listened
 * to and new values won't be written to the Part.
 *
 * [1]: https://github.com/tc39/proposal-async-iteration
 *
 * @param value An async iterable
 * @param mapper An optional function that maps from (value, index) to another
 *     value. Useful for generating templates for each item in the iterable.
 */
export declare const asyncAppend: <T>(value: AsyncIterable<T>, mapper?: ((v: T, index?: number | undefined) => unknown) | undefined) => (part: Part) => Promise<void>;
