Device token management in Firebase - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the device token for push notifications.

Firebase

const messaging = firebase.messaging();
messaging.getToken({ vapidKey: '[1]' })
  .then((currentToken) => {
    if (currentToken) {
      console.log('Device token:', currentToken);
    } else {
      console.log('No registration token available.');
    }
  })
  .catch((err) => {
    console.log('An error occurred while retrieving token. ', err);
  });

Drag options to blanks, or click blank then click option'

AYOUR_PUBLIC_VAPID_KEY_HERE

BfirebaseConfig

CapiKey

DprojectId

Attempts:

3 left

💡 Hint

Common Mistakes

Using the entire firebaseConfig object instead of the vapidKey string.

Leaving the vapidKey empty or undefined.

The vapidKey is required to get the device token for push notifications in Firebase Cloud Messaging.

2fill in blank

medium

Complete the code to save the device token to Firestore under the user's document.

Firebase

const db = firebase.firestore();
const userId = 'user123';
const token = [1];

db.collection('users').doc(userId).set({
  deviceToken: token
}, { merge: true });

Drag options to blanks, or click blank then click option'

AcurrentToken

BuserToken

CmessagingToken

DdeviceId

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable name that was not defined or assigned the token value.

Confusing device ID with device token.

The variable currentToken holds the device token retrieved from Firebase Messaging.

3fill in blank

hard

Fix the error in the code to correctly listen for token refresh events.

Firebase

messaging.[1](() => {
  messaging.getToken().then((refreshedToken) => {
    console.log('Token refreshed:', refreshedToken);
  }).catch((err) => {
    console.log('Unable to retrieve refreshed token ', err);
  });
});

Drag options to blanks, or click blank then click option'

AonTokenRefreshListener

BonTokenChanged

ConTokenUpdate

DonTokenRefresh

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect or non-existent method names for token refresh events.

Not handling the promise returned by getToken().

The correct Firebase Messaging method to listen for token refresh is onTokenRefresh.

4fill in blank

hard

Fill in the blank to correctly unsubscribe from push notifications and delete the token.

Firebase

messaging.[1](currentToken).then(() => {
  console.log('Token deleted and unsubscribed successfully.');
}).catch((err) => {
  console.log('Error unsubscribing or deleting token:', err);
});

Drag options to blanks, or click blank then click option'

Aunsubscribe

BdeleteToken

CremoveToken

DstopNotifications

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-existent methods like unsubscribe, removeToken or stopNotifications.

Forgetting to pass the currentToken.

Deleting the token using deleteToken unsubscribes from push notifications (including topics) and deletes the token.

5fill in blank

hard

Fill all three blanks to update the device token in Firestore only if the new token is different.

Firebase

const db = firebase.firestore();
const userId = 'user456';
const newToken = [1];

const userRef = db.collection('users').doc(userId);
userRef.get().then((doc) => {
  if (doc.exists && doc.data().deviceToken [2] [3]) {
    return userRef.update({ deviceToken: newToken });
  }
}).then(() => {
  console.log('Device token updated if changed.');
}).catch((error) => {
  console.error('Error updating token:', error);
});

Drag options to blanks, or click blank then click option'

AcurrentToken

B!==

C===

DnewToken

Attempts:

3 left

💡 Hint

Common Mistakes

Using equality operator instead of inequality.

Mixing up variable names for tokens.

The code compares the existing deviceToken with the newToken and updates only if they are different.

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