Javascript 如何使用Angular 7&；FCM（Firebase云消息）

我目前正在根据firebase-messaging-sw.js和messaging.service.ts接收到的推送通知，实现一个通知计数器。 我在messaging.service.ts（前台通知）中计算了通知数，并使用Behavior Subject将此通知的值发送到我的主要组件，在这里我可以显示这些新通知的数量（当我们在应用程序中时收到推送通知），但我现在正在努力如何发送（自动通知）firebase-messaging-sw.js（js文件）中计算的后台通知对我的主要组件（TypeScript文件）的值

firebase-messaging-sw.js

// Give the service worker access to Firebase Messaging.
// Note that you can only use Firebase Messaging here, other Firebase libraries
// are not available in the service worker.
importScripts('https://www.gstatic.com/firebasejs/5.5.0/firebase-app.js');
importScripts('https://www.gstatic.com/firebasejs/5.5.0/firebase-messaging.js');

// Initialize the Firebase app in the service worker by passing in the
// messagingSenderId.
firebase.initializeApp({
    messagingSenderId: 'MY-SENDER-ID'
});

// Retrieve an instance of Firebase Messaging so that it can handle background
// messages.
const messaging = firebase.messaging();
let amountOfNotifications = 0;

messaging.setBackgroundMessageHandler(function(payload) {
    if (payload.data.notification_type === 'message_001') {
        amountOfNotifications = amountOfNotifications + 1;
        console.log('amount of background notifications', amountOfNotifications);
        // how to emit amoutOfNotifications to another typescript component???
    }
    // here you can override some options describing what's in the message;
    // however, the actual content will come from the Webtask
    const notificationOptions = {
        body: 'New activity'
    };
    return self.registration.showNotification('Example App', notificationOptions);
});