import { Update } from '../types';
/**
 * Updates fields in the document referred to by this `DocumentReference`.
 * The update will fail if applied to a document that does not exist.
 *
 * Nested fields can be updated by providing dot-separated field path
 * strings.
 *
 * @param data An object containing the fields and values with which to
 * update the document.
 * @param precondition A Precondition to enforce on this update.
 * @throws Error If the provided input is not valid Firestore data.
 * @return A Promise resolved with the write time of this update.
 */
export declare const updateDoc: Update;