Push notifications with FCM in React Native - Build, Publish & Deploy

Build & Publish - Push notifications with FCM

Performance Impact

Using Firebase Cloud Messaging (FCM) for push notifications has minimal impact on app frame rate and memory. Notifications are handled by the system in the background, so your app's UI stays smooth at 60fps. However, frequent or heavy notifications can increase battery use and network data consumption.

Optimization Tips

To keep your app fast and responsive, avoid processing heavy tasks directly when a notification arrives. Instead, use background handlers efficiently and defer complex work until the app is active. Limit notification payload size to under 4KB to reduce network load and latency.

App Size and Startup Time

Adding FCM requires including Firebase SDKs, which can increase your app size by about 5-10MB. Use tools like Proguard (Android) and bitcode (iOS) to shrink the final bundle. The SDK does not significantly affect startup time since it initializes asynchronously.

iOS vs Android Differences

On iOS, you must request user permission to show notifications and configure APNs certificates in Firebase. iOS handles notification display and actions differently, requiring specific payload keys. Android requires adding Firebase configuration files and setting up notification channels for Android 8.0+ to control notification behavior.

Store Review Guidelines

• Apple App Store: Must request user consent for notifications and explain usage clearly in the permission prompt.
• Google Play Store: Follow policies on user privacy and data usage; disclose notification use in your privacy policy.
• Both stores require your app to handle notifications responsibly without spamming users.

Self-Check

Your app takes 5 seconds to load this screen. What's likely wrong?

• Firebase SDK initialization blocking the main thread.
• Heavy processing triggered by notification handlers on startup.
• Large notification payloads causing delays.

Key Result

FCM push notifications add minimal UI overhead but require careful setup for permissions and payload size to maintain smooth 60fps performance and comply with store policies.

Practice

1. What is the main purpose of Firebase Cloud Messaging (FCM) in a React Native app?

easy

A. To create UI components

B. To store user data locally

C. To send push notifications to the app users

D. To manage app navigation

Solution

1. Step 1: Understand FCM's role

   FCM is a service designed to send push notifications to apps.

2. Step 2: Compare options

   Only To send push notifications to the app users describes sending push notifications, which is FCM's main purpose.

3. Final Answer:

   To send push notifications to the app users -> Option C

4. Quick Check:

   FCM = Push notifications [OK]

Hint: FCM is about messaging, not UI or storage [OK]

Common Mistakes:

• Confusing FCM with local data storage
• Thinking FCM manages UI or navigation
• Assuming FCM is for database operations

2. Which React Native Firebase method is used to get the device token for FCM push notifications?

easy

A. messaging().requestPermission()

B. messaging().getToken()

C. messaging().sendMessage()

D. messaging().subscribeToTopic()

Solution

1. Step 1: Identify token retrieval method

   The method to get the device token is messaging().getToken().

2. Step 2: Eliminate other options

   requestPermission() asks user permission, sendMessage() sends messages, subscribeToTopic() subscribes to topics.

3. Final Answer:

   messaging().getToken() -> Option B

4. Quick Check:

   Get token = getToken() [OK]

Hint: Get token with getToken(), not requestPermission() [OK]

Common Mistakes:

• Using requestPermission() to get token
• Confusing sendMessage() with token retrieval
• Mixing subscribeToTopic() with token methods

3. What will be the output of this code snippet in a React Native app using FCM?

import messaging from '@react-native-firebase/messaging';

async function getToken() {
  const token = await messaging().getToken();
  console.log(token);
}

getToken();

medium

A. Logs the device's FCM token string to the console

B. Throws a syntax error due to missing await

C. Logs 'undefined' because getToken() returns nothing

D. Throws a runtime error because messaging() is undefined

Solution

1. Step 1: Analyze async function behavior

   The function awaits messaging().getToken(), which returns the device token string.

2. Step 2: Understand console.log output

   It logs the token string, not undefined or error, assuming messaging is imported correctly.

3. Final Answer:

   Logs the device's FCM token string to the console -> Option A

4. Quick Check:

   getToken() returns token string [OK]

Hint: Await getToken() to get token string, then log it [OK]

Common Mistakes:

• Forgetting await causing Promise logged
• Assuming getToken() returns undefined
• Not importing messaging correctly

4. You wrote this code to request permission for notifications but it doesn't work as expected:

import messaging from '@react-native-firebase/messaging';

messaging().requestPermission();

What is the likely problem?

medium

A. requestPermission() is not a valid method

B. You need to import notifications instead of messaging

C. You must call getToken() before requestPermission()

D. You forgot to await the requestPermission() call

Solution

1. Step 1: Check async method usage

   requestPermission() returns a Promise and should be awaited to complete permission request.

2. Step 2: Identify missing await effect

   Without await, the permission request may not finish before next steps, causing unexpected behavior.

3. Final Answer:

   You forgot to await the requestPermission() call -> Option D

4. Quick Check:

   Await async calls like requestPermission() [OK]

Hint: Always await async permission requests [OK]

Common Mistakes:

• Not awaiting async permission calls
• Thinking requestPermission() is invalid
• Calling getToken() before permission

5. You want to send a push notification only if the user has granted permission. Which code snippet correctly checks permission and then gets the FCM token in React Native?

hard

A. const authStatus = await messaging().requestPermission();
if (authStatus === messaging.AuthorizationStatus.AUTHORIZED) {
const token = await messaging().getToken();
console.log(token);
}

B. const token = await messaging().getToken();
if (token) {
await messaging().requestPermission();
console.log(token);
}

C. await messaging().getToken();
await messaging().requestPermission();
console.log('Permission and token done');

D. messaging().requestPermission();
messaging().getToken();
console.log('Permissions requested and token fetched');

Solution

1. Step 1: Check permission before token

   const authStatus = await messaging().requestPermission(); if (authStatus === messaging.AuthorizationStatus.AUTHORIZED) { const token = await messaging().getToken(); console.log(token); } requests permission and checks if authorized before getting token.

2. Step 2: Verify async and order correctness

   const authStatus = await messaging().requestPermission(); if (authStatus === messaging.AuthorizationStatus.AUTHORIZED) { const token = await messaging().getToken(); console.log(token); } awaits both calls and uses correct AuthorizationStatus check.

3. Final Answer:

   const authStatus = await messaging().requestPermission(); if (authStatus === messaging.AuthorizationStatus.AUTHORIZED) { const token = await messaging().getToken(); console.log(token); } -> Option A

4. Quick Check:

   Check permission first, then get token [OK]

Hint: Request permission first, then get token if authorized [OK]

Common Mistakes:

• Getting token before permission
• Not awaiting async calls
• Ignoring authorization status check