Firebase Admin SDK (Node.js) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

What is the output of this Firebase Admin SDK code snippet?

Consider this Node.js code using Firebase Admin SDK to fetch a user by UID:

import admin from 'firebase-admin';

admin.initializeApp();

async function getUser() {
  try {
    const userRecord = await admin.auth().getUser('nonexistentUID');
    console.log(userRecord.uid);
  } catch (error) {
    console.log(error.code);
  }
}

getUser();

What will be printed to the console?

Firebase

import admin from 'firebase-admin';

admin.initializeApp();

async function getUser() {
  try {
    const userRecord = await admin.auth().getUser('nonexistentUID');
    console.log(userRecord.uid);
  } catch (error) {
    console.log(error.code);
  }
}

getUser();

A SyntaxError

B auth/user-not-found

C undefined

D null

💡 Hint

Think about what happens when you request a user that does not exist in Firebase Authentication.

The Firebase Admin SDK throws an error with code auth/user-not-found when trying to get a user that does not exist. The catch block logs this error code.

❓ Configuration

intermediate

Which option correctly initializes Firebase Admin SDK with a service account JSON file?

You want to initialize Firebase Admin SDK in Node.js using a service account JSON file located at ./serviceAccountKey.json. Which code snippet correctly does this?

A

const admin = require('firebase-admin');
const serviceAccount = require('./serviceAccountKey.json');

admin.initializeApp({
  credential: admin.credential.cert(serviceAccount)
});

B

import admin from 'firebase-admin';

admin.initializeApp({
  credential: admin.credential.applicationDefault()
});

C

import admin from 'firebase-admin';
import serviceAccount from './serviceAccountKey.json' assert { type: 'json' };

admin.initializeApp({
  credential: admin.credential.cert(serviceAccount)
});

D

import admin from 'firebase-admin';

admin.initializeApp({
  credential: admin.credential.cert('./serviceAccountKey.json')
});

💡 Hint

Use ES modules import syntax and ensure the JSON file is imported correctly.

In ES modules, JSON files must be imported with assert { type: 'json' }. Then pass the imported JSON object to admin.credential.cert(). Option C does this correctly.

❓ Architecture

advanced

Which Firebase Admin SDK feature best supports sending notifications to multiple devices efficiently?

You want to send a push notification to thousands of devices using Firebase Admin SDK in Node.js. Which approach is best to optimize performance and cost?

A Call <code>admin.messaging().send()</code> individually for each device token in a loop.

B Send notifications via Firebase Realtime Database triggers only.

C Use <code>admin.messaging().sendToDevice()</code> with a single token repeatedly.

D Use <code>admin.messaging().sendMulticast()</code> to send to up to 500 tokens at once.

💡 Hint

Look for a method that supports batch sending to multiple tokens.

sendMulticast() allows sending a message to up to 500 device tokens in one call, which is efficient for large scale notifications. Sending individually (A) is inefficient. Option D is unrelated to sending messages directly. Option D sends to one token repeatedly, which is inefficient.

❓ security

advanced

What is the safest way to manage Firebase Admin SDK credentials in a production Node.js app?

You deploy a Node.js app using Firebase Admin SDK. Which practice ensures your service account credentials remain secure?

A Store the service account JSON file in environment variables or a secure secrets manager and load it at runtime.

B Commit the service account JSON file to the public GitHub repository for easy access.

C Hardcode the service account credentials directly in the source code.

D Share the service account JSON file via email to all developers.

💡 Hint

Think about how to keep sensitive data out of source code and public repos.

Storing credentials in environment variables or a secure secrets manager keeps them out of source code and version control, reducing risk of leaks. Committing to public repos or hardcoding exposes credentials. Sharing via email is insecure.

🧠 Conceptual

expert

What error will this Firebase Admin SDK code produce and why?

Analyze this Node.js code snippet:

import admin from 'firebase-admin';

admin.initializeApp();

async function createUser() {
  const user = await admin.auth().createUser({
    email: '[e-mail]',
    emailVerified: true,
    password: 'short',
  });
  console.log(user.uid);
}

createUser();

What error will occur when running this code and why?

Firebase

import admin from 'firebase-admin';

admin.initializeApp();

async function createUser() {
  const user = await admin.auth().createUser({
    email: '[e-mail]',
    emailVerified: true,
    password: 'short',
  });
  console.log(user.uid);
}

createUser();

A auth/invalid-password - Password must be at least 6 characters long.

B auth/email-already-exists - Email is already registered.

C auth/invalid-email - Email format is incorrect.

D No error, user is created successfully.

💡 Hint

Check Firebase password requirements for creating users.

Firebase requires passwords to be at least 6 characters. The password 'short' has 5 characters, so auth/invalid-password error is thrown.