index.js

const express = require("express");
const app = express();
const bodyParser = require('body-parser');
const admin = require('firebase-admin');
const serviceAccount = require("./serviceAccountKey.json");

var jsonParser = bodyParser.json()
app.use(bodyParser.urlencoded({
  extended:true
}));

admin.initializeApp({
  credential: admin.credential.cert(serviceAccount)
});


app.post('/sendChatNotification', jsonParser, async (req, res) => {
  const notificationInfo = req.body;
 
  // Firebase push token is saved in Firestore
  const user_doc = await admin.firestore().doc(`ChatUsers/` + notificationInfo.reciver_info).get();
  
  if (user_doc.exists) {
 
    const userData = user_doc.data();
    
    // reciver push token
    if (userData.pushToken) {
      
      // updating icon badge number
      const badgeNumber = userData.notificationCount + 1;
      
      // updating badge number in Firestore document
      admin.firestore().doc(`ChatUsers/` + notificationInfo.reciver_info).update({notificationCount: badgeNumber});
      
      await push.sendChatAppMessage([userData.pushToken], badgeNumber).then((messageRes) => {
        res.send({
          error: false,
          message: 'OK'
        });
      });
    } else {
      res.send({
        error: false,
        message: 'No Push token'
      })
    }
  } else {
    res.send({
      error: true,
      message: 'No such user'
    })
  }
})


app.listen(route, () => {
    console.log("Server Started at", process.env.PORT || 3000);
});