Firestore Functions: handle map value - node.js

Question

First of all I have to say that I have and intermediate experience on Java and very very basical with JS.
I'm trying to remove expired tokens from my database, for achieve that I did:
function sendNotificationToUser(payload, userSnapshot) {
const userId = userSnapshot.id;
const user = userSnapshot.data();
let tokenMap = user.tokens;
const tokens = Object.keys(tokenMap);
const options = {priority: "high"};
admin.messaging().sendToDevice(tokens, payload, options).then(response => {
// For each message check if there was an error.
response.results.forEach((result, index) => {
const error = result.error;
if (error) {
// Cleanup the tokens who are not registered anymore.
if (error.code === 'messaging/invalid-registration-token' || error.code === 'messaging/registration-token-not-registered') {
tokenMap.delete(tokens[index]);
}
} else{
console.log("Sent to user: ", user.name, " " ,user.surname, " notification: ", payload, " tokens: ", tokens[index]);
}
});
usersRef.doc(userId).update({
tokens: tokenMap
});
});
}
No problem to get the keys of the tokenMap, but looks like I can't remove entries with .delete(), since I got that in my Log:
TypeError: tokenMap.delete is not a function
at response.results.forEach (/user_code/index.js:127:36)
at Array.forEach (native)
at admin.messaging.sendToDevice.then.response (/user_code/index.js:122:26)
at process._tickDomainCallback (internal/process/next_tick.js:135:7)
What is the reason??

Answer 1

Solved:
delete tokensObj[tokensArray[index]];
Full code:
function sendNotificationToUser(payload, userSnapshot) {
const user = userSnapshot.data();
let tokensObj = user.tokens;
const tokensArray = Object.keys(tokensObj);
let toUpdate = false;
const options = {priority: "high"};
admin.messaging().sendToDevice(tokensArray, payload, options).then(response => {
// For each message check if there was an error.
response.results.forEach((result, index) => {
const error = result.error;
if (error) {
// Cleanup the tokens who are not registered anymore.
if (error.code === 'messaging/invalid-registration-token' || error.code === 'messaging/registration-token-not-registered') {
toUpdate = true;
delete tokensObj[tokensArray[index]];
}
} else {
console.log("Sent to user: ", user.name, " ", user.surname, " notification: ", payload, " token: ", tokensArray[index]);
}
});
if (toUpdate === true) {
userSnapshot.ref.update({ tokens: tokensObj }).catch(error => console.log(error));
}
});
}