import { Update } from '../types';
/**
 * Updates fields in the document referred to by the specified
 * `DocumentReference`. The update will fail if applied to a document that does
 * not exist.
 *
 * @param reference - A reference to the document to update.
 * @param data - An object containing the fields and values with which to
 * update the document. Fields can contain dots to reference nested fields
 * within the document.
 * @returns A `Promise` resolved once the data has been successfully written
 * to the backend (note that it won't resolve while you're offline).
 */
export declare const updateDoc: Update;