Firebase with React - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import Firebase configuration into your React app.

Firebase

import { initializeApp } from 'firebase/app';
const app = initializeApp([1]);

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

AappConfig

BfirebaseConfig

CconfigFirebase

DfirebaseApp

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong variable name for the config object.

Forgetting to import initializeApp from 'firebase/app'.

You need to pass the Firebase configuration object named firebaseConfig to initialize the app.

2fill in blank

medium

Complete the code to get a Firestore database instance in React.

Firebase

import { getFirestore } from 'firebase/firestore';
const db = getFirestore([1]);

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

AfirebaseConfig

Bdatabase

Cfirestore

Dapp

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the config object instead of the app instance.

Not importing getFirestore from 'firebase/firestore'.

You must pass the initialized Firebase app instance app to getFirestore to access Firestore.

3fill in blank

hard

Fix the error in the React useEffect hook to fetch Firestore documents.

Firebase

useEffect(() => {
  const fetchData = async () => {
    const querySnapshot = await getDocs(collection(db, [1]));
    // process data
  };
  fetchData();
}, []);

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

Adb.users

Busers

C'users'

DcollectionName

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the collection name without quotes causing a reference error.

Using incorrect variable names for the collection.

The collection name must be a string, so it should be wrapped in quotes like 'users'.

4fill in blank

hard

Fill both blanks to add a new document to Firestore with React.

Firebase

import { collection, [1] } from 'firebase/firestore';

const addUser = async (user) => {
  await [2](collection(db, 'users'), user);
};

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

AaddDoc

BsetDoc

CupdateDoc

DdeleteDoc

Attempts:

3 left

💡 Hint

Common Mistakes

Using setDoc without a document reference.

Confusing updateDoc or deleteDoc with addDoc.

You import and use addDoc to add a new document to a Firestore collection.

5fill in blank

hard

Fill all three blanks to update a Firestore document in React.

Firebase

import { doc, [1] } from 'firebase/firestore';

const updateUser = async (id, data) => {
  const userRef = doc(db, 'users', [2]);
  await [3](userRef, data);
};

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

AupdateDoc

Bid

DsetDoc

Attempts:

3 left

💡 Hint

Common Mistakes

Using setDoc instead of updateDoc when only updating fields.

Passing wrong variable names for the document ID.

You import updateDoc, use the id variable for the document ID, and call updateDoc to update the document.

Practice

1. What is the main purpose of using Firebase with React in app development?

easy

A. To replace React's state management

B. To style React components with CSS

C. To compile React code faster

D. To add backend features like database and authentication easily

Solution

1. Step 1: Understand Firebase role

   Firebase provides backend services like database and user authentication.

2. Step 2: Understand React role

   React handles the user interface and frontend logic.

3. Final Answer:

   To add backend features like database and authentication easily -> Option D

4. Quick Check:

   Firebase adds backend features [OK]

Hint: Firebase adds backend, React builds UI [OK]

Common Mistakes:

• Thinking Firebase is for styling
• Confusing Firebase with React state
• Assuming Firebase speeds up compilation

2. Which of the following is the correct way to initialize Firebase in a React app?

easy

A. import firebase from 'firebase'; firebase.init(config);

B. const app = new Firebase(config);

C. import { initializeApp } from 'firebase/app'; const app = initializeApp(config);

D. firebase.initialize(config);

Solution

1. Step 1: Check Firebase v9+ syntax

   Firebase modular SDK uses initializeApp from 'firebase/app'.

2. Step 2: Verify correct import and call

   import { initializeApp } from 'firebase/app'; const app = initializeApp(config); correctly imports and calls initializeApp with config.

3. Final Answer:

   import { initializeApp } from 'firebase/app'; const app = initializeApp(config); -> Option C

4. Quick Check:

   Use initializeApp from 'firebase/app' [OK]

Hint: Use modular import initializeApp from 'firebase/app' [OK]

Common Mistakes:

• Using old firebase namespace import
• Calling non-existent init or initialize methods
• Creating Firebase instance with new keyword

3. Given this React code snippet using Firebase Firestore:

import { useEffect, useState } from 'react';
import { getFirestore, collection, getDocs } from 'firebase/firestore';

function UsersList() {
  const [users, setUsers] = useState([]);
  useEffect(() => {
    const db = getFirestore();
    getDocs(collection(db, 'users')).then(snapshot => {
      const list = snapshot.docs.map(doc => doc.data().name);
      setUsers(list);
    });
  }, []);
  return <ul>{users.map(name => <li key={name}>{name}</li>)}</ul>;
}

What will this component display?

medium

A. A list of user names from the 'users' collection

B. An empty list because useEffect has no dependencies

C. A list of document IDs instead of names

D. A syntax error due to missing async keyword

Solution

1. Step 1: Analyze data fetching

   useEffect runs once, fetches 'users' collection documents, maps to their 'name' field.

2. Step 2: Analyze rendering

   Users state is set to list of names, rendered as list items in <ul>.

3. Final Answer:

   A list of user names from the 'users' collection -> Option A

4. Quick Check:

   Firestore docs mapped to names displayed [OK]

Hint: useEffect fetches once, maps docs to names [OK]

Common Mistakes:

• Thinking useEffect needs async keyword directly
• Confusing document IDs with data fields
• Assuming empty list due to empty dependency array

4. What is wrong with this React Firebase code snippet?

import { useEffect, useState } from 'react';
import { getFirestore, collection, getDocs } from 'firebase/firestore';

function Items() {
  const [items, setItems] = useState([]);
  useEffect(async () => {
    const db = getFirestore();
    const snapshot = await getDocs(collection(db, 'items'));
    setItems(snapshot.docs.map(doc => doc.data()));
  }, []);
  return <div>{items.length}</div>;
}

medium

A. getDocs requires a second argument for options

B. useEffect callback should not be async function

C. setItems should be called outside useEffect

D. useState initial value must be null

Solution

1. Step 1: Identify async useEffect issue

   React's useEffect callback cannot be async directly; it should call an async function inside.

2. Step 2: Confirm other parts

   getDocs usage and setItems inside useEffect are correct; initial state as empty array is valid.

3. Final Answer:

   useEffect callback should not be async function -> Option B

4. Quick Check:

   Async function inside useEffect, not async callback [OK]

Hint: Never make useEffect callback async directly [OK]

Common Mistakes:

• Making useEffect callback async directly
• Thinking getDocs needs extra arguments
• Believing setState must be outside useEffect

5. You want to build a React app that shows a live list of chat messages from Firebase Firestore. Which approach correctly updates the UI in real-time?

hard

A. Use Firestore's onSnapshot listener inside useEffect to update state on data changes

B. Call getDocs repeatedly every second inside useEffect to fetch new messages

C. Fetch messages once on component mount and never update state again

D. Use Firebase Realtime Database instead of Firestore for real-time updates

Solution

1. Step 1: Understand real-time update methods

   Firestore provides onSnapshot to listen to live data changes and update UI immediately.

2. Step 2: Compare options

   Use Firestore's onSnapshot listener inside useEffect to update state on data changes uses onSnapshot inside useEffect, which is best practice for real-time updates in React.

3. Final Answer:

   Use Firestore's onSnapshot listener inside useEffect to update state on data changes -> Option A

4. Quick Check:

   onSnapshot enables real-time UI updates [OK]

Hint: Use onSnapshot listener for live Firestore updates [OK]

Common Mistakes:

• Polling with getDocs wastes resources
• Fetching once misses updates
• Confusing Firestore with Realtime Database necessity