/**
 * @license
 * Copyright 2020 Google LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
import { MessagePayload, NextFn, Observer, Unsubscribe } from '../interfaces/public-types';
import { MessagingService } from '../messaging-service';
export declare function onBackgroundMessage(messaging: MessagingService, nextOrObserver: NextFn<MessagePayload> | Observer<MessagePayload>): Unsubscribe;