Upload progress monitoring in Firebase - Mini Project: Build & Apply

Upload Progress Monitoring with Firebase Storage

📖 Scenario: You are building a web app that allows users to upload files to Firebase Storage. You want to show users how much of their file has uploaded in real time, so they know the progress.

🎯 Goal: Create a Firebase Storage upload process that tracks and displays the upload progress percentage.

📋 What You'll Learn

Initialize Firebase Storage reference for a file upload

Create a variable to hold the file to upload

Use the uploadBytesResumable method to start the upload

Add an event listener to track upload progress and update a progress variable

💡 Why This Matters

🌍 Real World

Uploading files with progress feedback is common in web apps like photo sharing, document management, and backups.

💼 Career

Understanding upload progress monitoring is essential for frontend and backend developers working with cloud storage services.

1

Set up the file to upload

Create a variable called file and assign it the value selectedFile which represents the file chosen by the user.

Firebase

# Create a variable called file and assign selectedFile
# Your code here

Hint

Use const file = selectedFile; to hold the file object.

2

Create a Firebase Storage reference

Create a variable called storageRef and assign it the Firebase Storage reference for the path uploads/${file.name} using ref(storage, `uploads/${file.name}`).

Firebase

const file = selectedFile;
// Create a storageRef for uploads/${file.name}
# Your code here

Hint

Use ref(storage, `uploads/${file.name}`) to create the storage reference.

3

Start the upload and track progress

Create a variable called uploadTask and assign it the result of uploadBytesResumable(storageRef, file). Then add an event listener on uploadTask for the 'state_changed' event. Inside the listener, calculate the upload progress percentage as (snapshot.bytesTransferred / snapshot.totalBytes) * 100 and assign it to a variable called progress.

Firebase

const file = selectedFile;
const storageRef = ref(storage, `uploads/${file.name}`);
// Start upload and track progress
# Your code here

Hint

Use uploadBytesResumable to start the upload and uploadTask.on('state_changed', callback) to track progress.

4

Complete the upload progress monitoring

Inside the 'state_changed' event listener, add a console log statement that outputs the text Upload is ${progress}% done using a template literal. This will show the upload progress percentage in the console.

Firebase

const file = selectedFile;
const storageRef = ref(storage, `uploads/${file.name}`);
const uploadTask = uploadBytesResumable(storageRef, file);
uploadTask.on('state_changed', (snapshot) => {
  const progress = (snapshot.bytesTransferred / snapshot.totalBytes) * 100;
  // Log upload progress
  # Your code here
});

Hint

Use console.log(`Upload is ${progress}% done`); to show progress.

Practice

1. What does the state_changed event in Firebase Storage upload tasks help you monitor?

easy

A. The number of files in storage

B. The download speed of the file

C. The file size before upload

D. The progress of the file upload

Solution

1. Step 1: Understand the purpose of state_changed

   The state_changed event triggers updates during the upload process.

2. Step 2: Identify what is monitored

   This event provides progress updates, such as bytes transferred and total bytes.

3. Final Answer:

   The progress of the file upload -> Option D

4. Quick Check:

   Upload progress = state_changed event [OK]

Hint: Remember: state_changed tracks upload progress [OK]

Common Mistakes:

• Confusing upload progress with download speed
• Thinking it tracks file size before upload
• Assuming it counts files in storage

2. Which of the following is the correct way to attach a listener for upload progress in Firebase Storage using JavaScript?

easy

A. uploadTask.on('state_changed', progressCallback)

B. uploadTask.listen('progress', progressCallback)

C. uploadTask.addEventListener('upload', progressCallback)

D. uploadTask.track('state_change', progressCallback)

Solution

1. Step 1: Recall Firebase Storage upload syntax

   The method to listen for upload events is on with event name state_changed.

2. Step 2: Match correct method and event

   Only uploadTask.on('state_changed', progressCallback) is valid syntax.

3. Final Answer:

   uploadTask.on('state_changed', progressCallback) -> Option A

4. Quick Check:

   Use .on('state_changed') for progress [OK]

Hint: Use .on('state_changed') to monitor upload progress [OK]

Common Mistakes:

• Using non-existent methods like listen or track
• Wrong event names like 'progress' or 'upload'
• Confusing event listener syntax with DOM events

3. Given the following code snippet, what will be logged if 500 bytes out of 1000 bytes are uploaded?

uploadTask.on('state_changed', (snapshot) => {
  const progress = (snapshot.bytesTransferred / snapshot.totalBytes) * 100;
  console.log(`Upload is ${progress}% done`);
});

medium

A. Upload is 0.5% done

B. Upload is 50% done

C. Upload is 500% done

D. Upload is 100% done

Solution

1. Step 1: Calculate progress percentage

   Progress = (500 / 1000) * 100 = 50%

2. Step 2: Understand console output

   The console logs: "Upload is 50% done".

3. Final Answer:

   Upload is 50% done -> Option B

4. Quick Check:

   Progress = bytesTransferred / totalBytes * 100 [OK]

Hint: Divide bytesTransferred by totalBytes, multiply by 100 [OK]

Common Mistakes:

• Confusing bytesTransferred with percentage
• Multiplying by 100 twice
• Using integer division without decimal

4. You wrote this code to monitor upload progress but it never logs anything:

uploadTask.on('state_change', (snapshot) => {
  const progress = (snapshot.bytesTransferred / snapshot.totalBytes) * 100;
  console.log(`Upload is ${progress}% done`);
});

What is the error?

medium

A. The event name should be 'state_changed', not 'state_change'

B. The callback function is missing a return statement

C. You must use uploadTask.addListener instead of on

D. The progress calculation formula is incorrect

Solution

1. Step 1: Check event name spelling

   The correct event name is 'state_changed', not 'state_change'.

2. Step 2: Understand impact of wrong event name

   Using wrong event name means callback never triggers, so no logs appear.

3. Final Answer:

   The event name should be 'state_changed', not 'state_change' -> Option A

4. Quick Check:

   Event name must be exact 'state_changed' [OK]

Hint: Check event spelling: 'state_changed' not 'state_change' [OK]

Common Mistakes:

• Misspelling event names
• Expecting logs without callback firing
• Confusing method names like addListener vs on

5. You want to display upload progress as a percentage and also show a message when upload completes. Which code snippet correctly implements this using Firebase Storage's state_changed event?

hard

A. uploadTask.on('progress', snapshot => {
const progress = (snapshot.bytesTransferred / snapshot.totalBytes) * 100;
console.log(`Upload is ${progress}% done`);
});

B. uploadTask.on('state_changed', snapshot => {
console.log('Upload complete!');
});

C. uploadTask.on('state_changed', snapshot => {
const progress = (snapshot.bytesTransferred / snapshot.totalBytes) * 100;
console.log(`Upload is ${progress}% done`);
}, error => {
console.error(error);
}, () => {
console.log('Upload complete!');
});

D. uploadTask.on('state_changed', () => {
console.log('Upload is done');
});

Solution

1. Step 1: Use correct event and callbacks

   The state_changed event accepts three callbacks: progress, error, and completion.

2. Step 2: Verify progress calculation and completion message

   uploadTask.on('state_changed', snapshot => { const progress = (snapshot.bytesTransferred / snapshot.totalBytes) * 100; console.log(`Upload is ${progress}% done`); }, error => { console.error(error); }, () => { console.log('Upload complete!'); }); calculates progress and logs completion correctly; others miss callbacks or use wrong event.

3. Final Answer:

   uploadTask.on('state_changed', snapshot => { const progress = (snapshot.bytesTransferred / snapshot.totalBytes) * 100; console.log(`Upload is ${progress}% done`); }, error => { console.error(error); }, () => { console.log('Upload complete!'); }); -> Option C

4. Quick Check:

   Use three callbacks with 'state_changed' event [OK]

Hint: Use three callbacks with 'state_changed' for progress and completion [OK]

Common Mistakes:

• Using wrong event names like 'progress'
• Missing completion callback
• Logging completion inside progress callback