Send multiple firebase cloud messaging on one functions

Question

I have a data like this:

notification
    |----event01
             |---- token : "gdTh21dG705ysFA91..."
             |---- timestamp : 1513335600000
             |---- name : "Name Event A"
             |---- etc
    |----event02
             |---- token : "dG7058J1L8I:APA91..."
             |---- timestamp : 1513335600000
             |---- name : "Name Event B"
             |---- etc
    |----event03
             |---- token : "dG7058J1L8I:APA91..."
             |---- timestamp : 1513355000000
             |---- name : "Name Event C"
             |---- etc

I need to send FCM to user with token when timestamp has come, there will be more than 1 event with same timestamp but different name , so I can't just send the message using array of token.

I try to send the message like this, but if there is more than 1 event with same timestamp, only first message sent, without error.

how I can send all message with one functions, the event with same timestamp can be 2,3,4... or 100.

// Runs Promises in a pool that limits their concurrency.
const promisePool = require('es6-promise-pool');
const PromisePool = promisePool.PromisePool;

// Maximum concurrent message sending.
const MAX_CONCURRENT = 3;

/**
 * Send notification to user based on timestamp
 * Triggered when /variable/notification node updated
 * The node updated by C# service when the event is starting
 */
exports.sendStartNotification = functions.database.ref('/variables/notification').onUpdate(event => {
    const epoch = event.data.val();

    return admin.database().ref('/notification').orderByChild('timestamp').equalTo(epoch).once('value').then(snapshot => {
        // Use a pool so that we send maximum `MAX_CONCURRENT` notification in parallel.
        const promisePool = new PromisePool(() => {
            snapshot.forEach(childSnapshot => {

                let notif = childSnapshot.val();
                if (notif.token !== null && notif.token !== undefined && notif.token !== '') {
                    let payload = {
                        data: {
                            key: childSnapshot.key,
                            title: `Event ${notif.name} started`,
                            body: `Please check-in`
                        }
                    };

                    // Send the message
                    return admin.messaging().sendToDevice(notif.token, payload).catch(error => {
                        console.log("Sending failed:", error);
                    });
                }
            });
        }, MAX_CONCURRENT);

        promisePool.start().then(() => {
            console.log(`Sending success ${epoch}`);
        });
    });
});

Answer 1

You're not returning a promise at the end of your code, which means it may be terminated at any time (or continue running longer than necessary).

return promisePool.start();

I've never used promise pools, so would definitely consider using a regular Promise.all() to see if that makes a difference:

var promises = [];
snapshot.forEach(childSnapshot => {

    let notif = childSnapshot.val();
    if (notif.token !== null && notif.token !== undefined && notif.token !== '') {
        let payload = {
            data: {
                key: childSnapshot.key,
                title: `Event ${notif.name} started`,
                body: `Please check-in`
            }
        };

        // Send the message
        promises.push(admin.messaging().sendToDevice(notif.token, payload));
    }
});
return Promise.all(promises);