Uploading files in Firebase - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

What happens when you upload a file with the same name to Firebase Storage?

You upload a file named image.png to Firebase Storage. Then you upload another file with the same name image.png to the same location. What is the result?

A The new file overwrites the existing file silently.

B Firebase Storage creates a new file with a unique name to avoid overwriting.

C The upload fails with an error about duplicate file name.

D Both files are stored and Firebase Storage merges their contents.

💡 Hint

Think about how cloud storage usually handles files with the same path.

Firebase Storage treats files by their full path. Uploading a file with the same path overwrites the existing file silently.

❓ security

intermediate

Which Firebase Storage security rule allows only authenticated users to upload files?

Choose the Firebase Storage security rule snippet that restricts file uploads to authenticated users only.

Firebase

rules_version = '2';
service firebase.storage {
  match /b/{bucket}/o {
    match /{allPaths=**} {
      allow write: if <condition>;
    }
  }
}

A request.auth == null

B resource.size < 1048576

C request.time < timestamp.date(2025, 1, 1)

D request.auth != null

💡 Hint

Authenticated users have a non-null request.auth object.

The condition request.auth != null ensures only signed-in users can write (upload) files.

❓ Configuration

advanced

What is the correct way to get a download URL after uploading a file in Firebase Storage using JavaScript?

After uploading a file to Firebase Storage, you want to get its public download URL. Which code snippet correctly does this?

Firebase

import { getStorage, ref, uploadBytes, getDownloadURL } from 'firebase/storage';

const storage = getStorage();
const storageRef = ref(storage, 'files/myFile.txt');

// Assume file is a File object from input
uploadBytes(storageRef, file).then((snapshot) => {
  // What goes here?
});

A getDownloadURL(snapshot.ref).then(url => console.log(url));

B storageRef.getDownloadURL().then(url => console.log(url));

C snapshot.downloadURL.then(url => console.log(url));

D uploadBytes.getDownloadURL(storageRef).then(url => console.log(url));

💡 Hint

Look at the Firebase Storage API for getting download URLs after upload.

The uploadBytes returns a snapshot with a ref property. Use getDownloadURL(snapshot.ref) to get the URL.

❓ Architecture

advanced

Which Firebase Storage architecture best supports large file uploads with resume capability?

You want to allow users to upload large files that can resume if interrupted. Which Firebase Storage upload method supports this?

A Split the file manually and upload parts with <code>uploadBytes()</code>.

B Use <code>uploadBytes()</code> method with retry logic in your code.

C Use <code>uploadBytesResumable()</code> method with progress listeners.

D Use Firebase Realtime Database to store file chunks.

💡 Hint

Firebase Storage has a built-in method for resumable uploads.

The uploadBytesResumable() method supports resumable uploads and progress monitoring natively.

✅ Best Practice

expert

What is the best practice to secure Firebase Storage uploads to prevent unauthorized overwrites?

You want to prevent users from overwriting files uploaded by others in Firebase Storage. Which security rule approach achieves this?

A Allow write only if the file size is less than 1MB.

B Allow write only if the file does not exist yet: <code>resource == null</code> and user is authenticated.

C Allow write only if the user is authenticated, ignoring file existence.

D Allow write only during business hours.

💡 Hint

Think about how to prevent overwriting existing files by checking their existence.

Checking resource == null ensures files cannot be overwritten once uploaded, combined with authentication.