Firebase Cloud Messaging + Cloud Functions

index.js

const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();

exports.sendLeaderboardMesssage = functions
  .database
  .ref('/leaderboard/{position}')
  .onUpdate((change) => {

    const oldPlayer = change.before.val();
    const newPlayer = change.after.val();
    
    // Exit if change is caused by old player moving up in leaderboard
    if (newPlayer.score <= oldPlayer.score) { return; }
    
    const payload = {
      notification: {
        title: `${oldPlayer.handle}, ${newPlayer.handle} just beat your score!`,
        body: 'Play now to get back on the leaderboard',
      }
    };
    
    const databaseRoot = change.before.ref.root;
    return databaseRoot.child('users/' + oldPlayer.uId).once('value')
      .then(snapshot => {
        const fcmToken = snapshot.val().fcmToken;
        return admin.messaging().sendToDevice(fcmToken, payload);
      });
  });

Thank you for this Lauren 👍

You're welcome!

Thanks for code lauren! How can I use it with Firestore when my score is saved in structure like this?

score/{userId}/subject/{quizResultId}/

Hey @poojaba, thanks for the comment! It doesn't seem like your data is a high score board, rather it seems to be storing individual quiz results for each user. So you can't directly use this code. I recommend checking out documentation for database functions to learn how to write a function that suits your use case: https://firebase.google.com/docs/functions/database-events

Thanks for reply @laurenzlong. I have subject wise high scores at user document like this:

users/{userID}

fields (key - value):
history - 120
science - 150
total - 270