how to handle array of 'promis' - node.js

Question

I built a database that contains a list of users who receive messages from firebase with a request key. Every time a new request with status 'open' inserted, I am trying to sort them all by the value of 'Timestamp' and send it by this order to the receivers(each receiver will get one message).
if the list of receivers is empty I want to hold it, until another receiver will be added to the list and continue to the next request.
I am not sure how to send each 'promise' separately one after another-
exports.notificationListener=functions.database.ref('requests')
.onWrite(event=>{
const ref = event.data.ref;
let requests= [];
var query=ref.orderByChild('TimeStamp');
query.once('value',function(snap){
snap.forEach(request=>{
if(request.val().Status==OPEN)
requests.push(request.key);
});
});
for (let key of requests) {
return getOnlinReceiversToken().then(token=>{
let msg = {
data: {
source: key
}
};
return admin.messaging().sendToDevice(token, msg);
)};
}
});
function getOnlinReceiversToken() {
let result = new Promise((resolve, reject) => {
receiverRef.once('value', (snap) => {
resolve(snap);
},
(err) => {
reject(err);
});
});
return result.then(snap => {
snap.forEach(child => {
if(child.Status == ONLINE){
let token = helper.getToken(child.key,db);
break;
}
});
return token;
});
}

Answer 1

try something like this
var promisesArray = [];
for (let key of requests) {
var currentPromise = getOnlinReceiversToken().then(token=>{
let msg = {
data: {
source: key
}
};
return admin.messaging().sendToDevice(token, msg);
});
promisesArray.push(currentPromise);
}
return Promise.all(promisesArray);

Answer 2

You could use a function that calls itself to iterate through the promises sequentially to send them one after the other
function runPromise(index) {
// jump out of loop if there are no more requests
if (index >= requests.length) {
return console.log('finished!');
}
return getOnlinReceiversToken().then((token) => {
let msg = {
data: { source: key }
};
admin.messaging().sendToDevice(token, msg);
// iterate to the next item
return runPromise(index + 1);
}).catch((err) => {
// break out of loop when an error occurs
console.log(err);
});
}
runPromise(0);