Firebase Cloud Function to keep the community scores updated for my slide puzzle project at https://github.com/ashishbeck/slide_puzzle

index.js

const functions = require("firebase-functions");
const admin = require("firebase-admin");
admin.initializeApp();
const db = admin.firestore();
const FieldValue = admin.firestore.FieldValue;

exports.updateScores = functions.firestore
   .document("users/{userId}")
   .onUpdate((change, context) => {
      const newValue = change.after.data();
      const oldValue = change.before.data();
      const newMoves = newValue.moves;
      const newTimes = newValue.times;
      const oldMoves = oldValue.moves;
      const oldTimes = oldValue.times;
      const gridSize = ["three", "four"];
      gridSize.forEach(grid => {
         const newMove = newMoves[grid];
         const oldMove = oldMoves[grid];
         const newTime = newTimes[grid];
         const oldTime = oldTimes[grid];
         if (newMove != oldMove) {
            const isOldZero = oldMove == 0;
            let payload = {};
            payload[`${grid}.${newMove}`] = FieldValue.increment(1);
            if (!isOldZero) {
               payload[`${grid}.${oldMove}`] = FieldValue.increment(-1);
            }
            db.collection("community").doc("moves").update(payload);
            // console.log("data updated " + grid + ", " + JSON.stringify(payload));
         }
         if (newTime != oldTime) {
            const isOldZero = oldTime == 0;
            let payload = {};
            payload[`${grid}.${newTime}`] = FieldValue.increment(1);
            if (!isOldZero) {
               payload[`${grid}.${oldTime}`] = FieldValue.increment(-1);
            }
            db.collection("community").doc("times").update(payload);
         }
      });
   });