Firebase Cloud Function to trigger Firebase Messaging not sending Notification

I want to send a PushNotification via Cloud Messaging when a document is added inside a collection of a user called notifications. I am saving the token for the user as suggested in the docs in a arrayUnion in a field called messagingTokens.

Additionally the notification should only be sent if a field called isPushEnabled is true. With this information I build this cloud function and successfully deployed it:

const functions = require("firebase-functions");
const admin = require("firebase-admin");
const { onDocumentCreated } = require("firebase-functions/v2/firestore");
const { setGlobalOptions } = require("firebase-functions/v2");
admin.initializeApp();
// Set the maximum instances to 10 for all functions
setGlobalOptions({ maxInstances: 10 });
const notificationPath = "allUsers/{userId}/notifications/{notificationId}";
exports.sendNotification = onDocumentCreated(notificationPath, async (event) => {
functions.logger.log("New notificatin document was created"); 
const data = event.data.after.data();
const senderUid = data.senderUid;
const receiverUid = data.receiverUid;
const notificationOption = data.option;
functions.logger.log("Retrieved notification fields"); 
if (notificationOption === "receivedFriendRequest") {
functions.logger.log("Is option: receivedFriendRequest");
await onSentFriendRequest(senderUid, receiverUid);
}
});
async function onSentFriendRequest(ownerId, userId) {
// Get the owners details
const owner = await admin.firestore().collection("allUsers").doc(ownerId).get();
// Get the users details
const user = await admin.firestore().collection("allUsers").doc(userId).get();
const userHasNotificationsEnabled = user.data().isPushEnabled;
functions.logger.log("If this does not print, then your function is not being called");
if (!userHasNotificationsEnabled) {
functions.logger.log("User does not have push enabled");
return;
}
functions.logger.log("User has push enabled");
// Listing all tokens as an array.
tokens = user.data().messagingTokens;
// Send message to all tokens
const response = await admin.messaging().sendEachForMulticast({
tokens: tokens,
notification: {
title: "Neue Freundschaftsanfrage",
body: `${owner.data().username} möchte mit dir befreundet sein.`,
},
data: {
ownerId: ownerId,
userId: userId,
notificationOption: "receivedFriendRequest",
},
});
// For each message check if there was an error.
const tokensToRemove = [];
response.results.forEach((result, index) => {
const error = result.error;
if (error) {
functions.logger.error(
'Failure sending notification to',
tokens[index],
error
);
// Cleanup the tokens who are not registered anymore.
if (error.code === 'messaging/invalid-registration-token' ||
error.code === 'messaging/registration-token-not-registered') {
tokensToRemove.push(tokensSnapshot.ref.child(tokens[index]).remove());
}
}
});
return Promise.all(tokensToRemove);
}

Like I said, the deployment was successful. But when a document is added to the notifications-collection I get this from my logs:

Inside the Firebase-Console I see that the function was triggered, I get a TypeError.

What am I doing wrong here?
Let me know if you need more information.

EDIT

I had an error about maxScale which I could fix by adding this line inside my index.js-file:

    setGlobalOptions({maxInstances: 10})

and this inside my firebase.json:

  "frameworksBackend": {
"region": "us-central1",
"maxInstances": 10
}

I got it working. I had smaller issues in my code, like Typos, or the suggested improvements from the answers.

By following this Sample-Code and also looking into doc for sendEachForMultiCast and onDocumentCreated I was able to make it work with this code:

const functions = require("firebase-functions");
const admin = require("firebase-admin");
const { onDocumentCreated } = require("firebase-functions/v2/firestore");
const { setGlobalOptions } = require("firebase-functions/v2");
admin.initializeApp();
// Set the maximum instances to 10 for all functions
setGlobalOptions({ maxInstances: 10 });
const notificationPath = "allUsers/{userId}/notifications/{notificationId}";
exports.sendNotification = onDocumentCreated(notificationPath, async (event) => {
functions.logger.log("New notificatin document was created");
const snapshot = event.data;
if (!snapshot) {
console.log("No data associated with the event");
return;
}
const data = snapshot.data();
// access a particular field as you would any JS property
const name = data.name;
const senderUid = data.senderUid;
const receiverUid = data.receiverUid;
const notificationOption = data.option;
if (notificationOption === "recievedFriendRequest") {
await onSentFriendRequest(senderUid, receiverUid);
} else {
functions.logger.log(`is notificationOption: ${notificationOption}`);
}
});
async function onSentFriendRequest(ownerId, userId) {
// Get the owners details
const owner = await admin.firestore().collection("allUsers").doc(ownerId).get();
// Get the users details
const user = await admin.firestore().collection("allUsers").doc(userId).get();
const userHasNotificationsEnabled = user.data().isPushEnabled;
if (!userHasNotificationsEnabled) {
functions.logger.log("User does not have push enabled");
return;
}
// Listing all tokens as an array.
tokens = user.data().messagingTokens;
// Send message to all tokens
const response = await admin.messaging().sendEachForMulticast({
tokens: tokens,
notification: {
title: "Neue Freundschaftsanfrage",
body: `${owner.data().username} möchte mit dir befreundet sein.`,
},
data: {
ownerId: ownerId,
userId: userId,
notificationOption: "receivedFriendRequest",
},
});
functions.logger.log("Successflully send Notification");
// For each message check if there was an error.
const tokensToRemove = [];
response.responses.forEach((result, index) => {
const error = result.error;
if (error) {
functions.logger.error(
'Failure sending notification to',
tokens[index],
error
);
// Cleanup the tokens who are not registered anymore.
if (error.code === 'messaging/unregistered' || 
error.code === 'messaging/invalid-argument') {               
tokensToRemove.push(admin.firestore().collection("allUsers").doc(userId).update({
"messagingTokens": admin.firestore.FieldValue.arrayRemove(tokens[index])
}));
}
}
});
return Promise.all(tokensToRemove);
}

const admin = require('firebase-admin');
admin.initializeApp();

When working with Firebase Functions, you should always use the onCreate trigger to listen for document creations instead of the onDocumentCreated function, since it does not exist in the Firebase Functions SDK. Writing with an increased degree of complexity and variation can lead to much more interesting and engaging content, allowing readers to better understand and appreciate the words they are consuming.

exports.sendNotification = functions.firestore
.document(notificationPath)
.onCreate(async (snapshot, context) => {
// Retrieve the document data
const data = snapshot.data();
const senderUid = data.senderUid;
const receiverUid = data.receiverUid;
const notificationOption = data.notificationOption;
if (notificationOption === "receivedFriendRequest") {
await onSentFriendRequest(senderUid, receiverUid);
}
});

Updating user tokens in your code is essential. To retrieve a user's messagingTokens, the code needs to take a Firestore document snapshot and account for the messagingTokens field. To do that, user.data().messagingTokens must be used. Therefore, the code should be changed as follows: user.data().messagingTokens instead of user.messagingTokens.

const userHasNotificationsEnabled = user.data().isPushEnabled;
if (userHasNotificationsEnabled) {
const tokens = user.data().messagingTokens;
await admin.messaging().sendMulticast({
tokens: tokens,
notification: {
title: "Neue Freundschaftsanfrage",
body: `${owner.data().userName} möchte mit dir befreundet sein.`,
},
data: {
ownerId: ownerId,
userId: userId,
notificationOption: "receivedFriendRequest",
},
});
}

you can add console.log statement at relevant points.

console.log("User has push enabled");

Hope this helps!

From the docs, admin.messaging().send(message: Message, dryRun?: boolean) takes in 2 parameters, i.e, message and dryRun. It does not take the token. You should add the token to the message.

functions.logger.log("If this does not print, then your function is not being called");
if (!userHasNotificationsEnabled) {
functions.logger.log("User does not have push enabled");
return;
}
functions.logger.log("User has push enabled");
const message = {
notification: {
title: "Neue Freundschaftsanfrage",
body: owner.userName + " möchte mit dir befreundet sein.",
},
data: {
ownerId: ownerId,
userId: userId,
notificationOption: "recievedFriendRequest",
},
token: user.messagingTokens.first, // token should be a single string
};
functions.logger.log(message);
await admin.messaging().send(message);

Also, consider using .onCreate( instead of onDocumentCreated(