Device token management in Firebase - Mini Project: Build & Apply

Device Token Management with Firebase

📖 Scenario: You are building a mobile app that sends notifications to users. To do this, you need to manage device tokens securely and efficiently using Firebase Cloud Messaging (FCM).

🎯 Goal: Create a simple Firebase Cloud Function to store device tokens in Firestore, update them when needed, and delete tokens when users log out.

📋 What You'll Learn

Create a Firestore collection called deviceTokens to store tokens.

Write a Cloud Function to add a new device token to Firestore.

Write a Cloud Function to update an existing device token.

Write a Cloud Function to delete a device token when a user logs out.

💡 Why This Matters

🌍 Real World

Managing device tokens is essential for sending push notifications to users in mobile apps securely and efficiently.

💼 Career

This project teaches skills used by cloud engineers and backend developers working with Firebase to handle user device data and notifications.

1

Create Firestore collection and add device token

Create a Cloud Function called addDeviceToken that takes userId and token as parameters and adds a document to the deviceTokens collection with userId as the document ID and token as a field.

Firebase

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

// Create addDeviceToken function
// Your code here

Hint

Use functions.https.onCall to create the function. Use admin.firestore().collection('deviceTokens').doc(userId).set({ token: token }) to add the token.

2

Add update token configuration

Create a variable called updateOptions with the value { merge: true } to allow updating existing tokens without overwriting the whole document.

Firebase

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

exports.addDeviceToken = functions.https.onCall(async (data, context) => {
  const userId = data.userId;
  const token = data.token;
  await admin.firestore().collection('deviceTokens').doc(userId).set({ token: token });
  return { message: 'Token added successfully' };
});

// Create updateOptions variable
// Your code here

Hint

Define const updateOptions = { merge: true } to use later for updating tokens.

3

Create updateDeviceToken function

Create a Cloud Function called updateDeviceToken that takes userId and newToken as parameters and updates the token field in the deviceTokens collection using updateOptions to merge changes.

Firebase

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

const updateOptions = { merge: true };

exports.addDeviceToken = functions.https.onCall(async (data, context) => {
  const userId = data.userId;
  const token = data.token;
  await admin.firestore().collection('deviceTokens').doc(userId).set({ token: token });
  return { message: 'Token added successfully' };
});

// Create updateDeviceToken function
// Your code here

Hint

Use set with updateOptions to update the token without overwriting the whole document.

4

Create deleteDeviceToken function

Create a Cloud Function called deleteDeviceToken that takes userId as a parameter and deletes the corresponding document from the deviceTokens collection.

Firebase

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

const updateOptions = { merge: true };

exports.addDeviceToken = functions.https.onCall(async (data, context) => {
  const userId = data.userId;
  const token = data.token;
  await admin.firestore().collection('deviceTokens').doc(userId).set({ token: token });
  return { message: 'Token added successfully' };
});

exports.updateDeviceToken = functions.https.onCall(async (data, context) => {
  const userId = data.userId;
  const newToken = data.newToken;
  await admin.firestore().collection('deviceTokens').doc(userId).set({ token: newToken }, updateOptions);
  return { message: 'Token updated successfully' };
});

// Create deleteDeviceToken function
// Your code here

Hint

Use delete() on the document reference to remove the token.

Practice

1. What is the main purpose of a device token in Firebase Cloud Messaging?

easy

A. To store user passwords securely

B. To manage database access permissions

C. To track user location in real-time

D. To uniquely identify a device for sending notifications

Solution

1. Step 1: Understand device token role

   A device token is a unique identifier assigned to each device by Firebase to target messages.

2. Step 2: Match purpose with options

   Only To uniquely identify a device for sending notifications correctly describes the token's role in sending notifications to a specific device.

3. Final Answer:

   To uniquely identify a device for sending notifications -> Option D

4. Quick Check:

   Device token = unique device ID for messaging [OK]

Hint: Device tokens identify devices for messaging [OK]

Common Mistakes:

• Confusing tokens with passwords
• Thinking tokens track location
• Assuming tokens manage database access

2. Which Firebase method is used to delete a device token?

easy

A. firebase.messaging().clearToken()

B. firebase.messaging().removeToken()

C. firebase.messaging().deleteToken()

D. firebase.messaging().revokeToken()

Solution

1. Step 1: Recall Firebase token deletion method

   The correct method to delete a device token is deleteToken().

2. Step 2: Compare options with correct method

   Only firebase.messaging().deleteToken() matches the exact method name deleteToken().

3. Final Answer:

   firebase.messaging().deleteToken() -> Option C

4. Quick Check:

   Delete token method = deleteToken() [OK]

Hint: Delete tokens with deleteToken() method [OK]

Common Mistakes:

• Using removeToken() which does not exist
• Confusing clearToken() with deleteToken()
• Using revokeToken() which is invalid

3. Consider this code snippet:

const messaging = firebase.messaging();
const token = await messaging.getToken();
console.log(token);

What will be the output of console.log(token)?

medium

A. A unique string representing the device token

B. An error because getToken() requires parameters

C. Undefined because getToken() is not asynchronous

D. A boolean indicating token availability

Solution

1. Step 1: Understand getToken() behavior

   The getToken() method asynchronously returns a unique device token string.

2. Step 2: Analyze code output

   Since await is used, token holds the string token, so console.log prints that string.

3. Final Answer:

   A unique string representing the device token -> Option A

4. Quick Check:

   getToken() returns token string [OK]

Hint: getToken() returns a unique token string asynchronously [OK]

Common Mistakes:

• Thinking getToken() returns boolean
• Assuming getToken() needs parameters
• Ignoring async/await usage

4. You wrote this code to delete a device token:

firebase.messaging().deleteToken;

Why does this code fail to delete the token?

medium

A. deleteToken requires a token parameter which is missing

B. deleteToken is missing parentheses to call the function

C. deleteToken is not a valid Firebase method

D. deleteToken must be called on firebase.auth() instead

Solution

1. Step 1: Check method invocation syntax

   The code references deleteToken without parentheses, so the function is not called.

2. Step 2: Understand function call requirements

   To execute the function, parentheses () are required even if no parameters are passed.

3. Final Answer:

   deleteToken is missing parentheses to call the function -> Option B

4. Quick Check:

   Function calls need () to execute [OK]

Hint: Always use () to call functions like deleteToken() [OK]

Common Mistakes:

• Forgetting parentheses on method calls
• Assuming deleteToken needs parameters
• Calling deleteToken on wrong Firebase service

5. You want to send a notification only to devices of a specific user. Which is the best practice for managing device tokens in Firebase?

hard

A. Store each user's device tokens in a database linked to their user ID

B. Use a single global token for all users to simplify messaging

C. Delete tokens immediately after sending a notification

D. Generate new tokens manually for each notification

Solution

1. Step 1: Understand targeted messaging needs

   To send notifications to specific users, you must know their device tokens.

2. Step 2: Choose token management strategy

   Storing tokens linked to user IDs in a database allows targeted, reliable messaging.

3. Final Answer:

   Store each user's device tokens in a database linked to their user ID -> Option A

4. Quick Check:

   Link tokens to users for targeted notifications [OK]

Hint: Link tokens to user IDs in database for targeted messages [OK]

Common Mistakes:

• Using one token for all users
• Deleting tokens too soon
• Manually generating tokens instead of Firebase