I want to rewrite all documents in a collection with firebase functions

Question

I am developing an app in flutter. I would like to rewrite the　value of "life" field of all documents in the "users" collection of the Firestore to "10(int)" at 00:00 Tokyo time. I managed to write the code anyway, but I am completely clueless about JavaScript　and Functions, so it doesn't work.　　I would like to know how to correct it.　This is my code.

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

process.env.TZ = "Asia/Tokyo";

export const checkTimezone = functions.region('asia-northeast1').https.onRequest(async (req, res) => {
  console.info(process.env.TZ)
});

exports.timer = functions.pubsub.schedule('00***').onRun((context) => {
    functions.logger.info("timer1 start", {structuredData: true});
    admin.firestore().collection("users").get().then(function(querySnapshot){
        querySnapshot.forEach(function(doc){
            doc.ref.update({
                life:10
            });
        });
    })
});

Answer 1

The default timezone for Cloud Functions is America/Los_Angeles. You can set the timezone to Asia/Tokyo so the function will run at every midnight in Japan. Also, you must return a promise from the function to terminate it once the updates have been completed. Try refactoring to code as shown below:

const functions = require("firebase-functions");
const admin = require("firebase-admin");

admin.initializeApp();
const db = admin.firestore();

exports.timer = functions.pubsub
  .schedule("0 0 * * *")
  .timeZone("Asia/Tokyo")
  .onRun((context) => {
    functions.logger.info("timer1 start", {structuredData: true});

    const usersRef = db.collection("users");

    return usersRef.get().then((snapshot) => {
      const promises = [];

      snapshot.forEach((doc, i) => {
        promises.push(doc.ref.update({ life: 10 }));
      });

      return Promise.all(promises);
    });
  });