AppServer code for Push Notification

app.js

var firebase = require('firebase-admin');
var request = require('request');

// Fetch the service account key JSON file contents
var serviceAccount = require("path/to/serviceAccountKey.json");
var env = require("path/to/env.json");

// Your Firebase Cloud Messaging Server API key
var API_KEY = env.CLOUD_MESSAGE_API_KEY;

// Initialize the app with a service account, granting admin privileges
firebase.initializeApp({
  credential: firebase.credential.cert(serviceAccount),
  databaseURL: "https://<your database>.firebaseio.com/"
});
ref = firebase.database().ref();

function listenForNotificationRequests() {
  var requests = ref.child('notificationRequests');
  requests.on('child_added', function(requestSnapshot) {
    var request = requestSnapshot.val();
    sendNotificationToTopic(
      request.from_username,
      request.message,
      function() {
        console.log("Successfully sent!");
        requestSnapshot.ref.remove();
      }
    );
  }, function(error) {
    console.error(error);
  });
};

function sendNotificationToTopic(from_username, message, onSuccess) {
  // Send a message to devices subscribed to the provided topic.
  var topic = `/topics/list`;
  // https://firebase.google.com/docs/reference/admin/node/admin.messaging.NotificationMessagePayload
  var payload = {
    "notification": {
        title: "hello",
        body: `${from_username} ${message}`,
        icon: "new",
        sound: "default",
        clickAction: "fcm.ACTION.HELLO",
        // badge: '1'
    },
    data: {
      extra: "some_extra_data",
    }
  };
  
  var options = {
    collapseKey: 'demo',
    contentAvailable: true,
    priority: "high",
    timeToLive: 60 * 60 * 24 // Set the message as high priority and have it expire after 24 hours.
  };
  firebase.messaging().sendToTopic(topic, payload, options)
    .then(function(response) {
      // See the MessagingTopicResponse reference documentation for the
      // contents of response.
      console.log("Successfully sent message:", response);
      onSuccess();
    })
    .catch(function(error) {
      console.log("Error sending message:", error);
    });
}

// start listening
listenForNotificationRequests();