Upload progress monitoring in Firebase - Step-by-Step Execution

Process Flow - Upload progress monitoring

Start Upload

↓

Upload Begins

↓

Listen to Progress Event

↓

Calculate % Uploaded

↓

Update Progress UI

↓

Upload Complete?

No→Continue Upload

Yes↓

Upload Finished

This flow shows how an upload starts, progress events are listened to, progress percentage is calculated and UI updated until upload finishes.

Execution Sample

Firebase

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

This code uploads a file and logs the upload progress percentage as it changes.

Process Table

Step	Event Triggered	bytesTransferred	totalBytes	Progress %	Action Taken
1	Upload starts	0	1000	0	Upload begins, progress 0%
2	state_changed	200	1000	20	Log 'Upload is 20% done'
3	state_changed	500	1000	50	Log 'Upload is 50% done'
4	state_changed	800	1000	80	Log 'Upload is 80% done'
5	state_changed	1000	1000	100	Log 'Upload is 100% done', upload complete

💡 Upload completes when bytesTransferred equals totalBytes (1000), progress reaches 100%

Status Tracker

Variable	Start	After 1	After 2	After 3	After 4	Final
bytesTransferred	0	200	500	800	1000	1000
totalBytes	1000	1000	1000	1000	1000	1000
progress	0	20	50	80	100	100

Key Moments - 2 Insights

Why does progress sometimes jump in big steps instead of smoothly increasing?

Progress updates depend on the 'state_changed' events from Firebase, which may fire irregularly as chunks upload. See execution_table rows 2-4 where progress jumps from 20% to 50% to 80%.

What happens if totalBytes is zero or unknown?

If totalBytes is zero, dividing by zero causes progress calculation issues. Firebase usually provides totalBytes, but if missing, progress can't be calculated properly. This is why totalBytes is tracked constant in variable_tracker.

Visual Quiz - 3 Questions

Look at the execution_table, what is the progress % at step 3?

A 20%

B 80%

C 50%

D 100%

💡 Hint

Check the 'Progress %' column in execution_table row 3.

At which step does the upload complete?

A Step 4

B Step 5

C Step 3

D Step 2

💡 Hint

Look for when bytesTransferred equals totalBytes in execution_table.

If bytesTransferred was 400 at step 2 instead of 200, what would progress % be?

A 40%

B 20%

C 50%

D 80%

💡 Hint

Calculate (bytesTransferred / totalBytes) * 100 using variable_tracker values.

Concept Snapshot

Upload progress monitoring in Firebase:
- Use uploadTask.on('state_changed') to listen for progress
- Calculate progress as (bytesTransferred / totalBytes) * 100
- Update UI or log progress inside the event handler
- Upload completes when bytesTransferred equals totalBytes
- Progress events may fire irregularly, showing jumps

Full Transcript

This visual execution trace shows how Firebase upload progress monitoring works. The upload starts and triggers 'state_changed' events. Each event provides bytesTransferred and totalBytes. Progress percentage is calculated by dividing bytesTransferred by totalBytes and multiplying by 100. The progress is logged or shown in UI. The upload finishes when bytesTransferred equals totalBytes. The execution table tracks each step's bytesTransferred, totalBytes, and progress percent. Variable tracker shows how these values change over time. Key moments clarify why progress jumps and the importance of totalBytes. The quiz tests understanding of progress values at steps and calculations.