Reading data (once and listener) in Firebase - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to read data once from Firebase Realtime Database.

Firebase

firebase.database().ref('users').[1](snapshot => {
  console.log(snapshot.val());
});

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

Aonce

Bon

Cget

Dlisten

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'on' instead of 'once' causes continuous listening.

Using 'get' is not a method on the reference in this context.

The once method reads data a single time from the database.

2fill in blank

medium

Complete the code to listen for real-time updates on the 'messages' node.

Firebase

firebase.database().ref('messages').[1]('value', snapshot => {
  console.log(snapshot.val());
});

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Aget

Bon

Conce

Dfetch

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'once' reads data only once, not continuously.

Using 'get' or 'fetch' are not valid methods here.

The on method sets up a listener for real-time updates.

3fill in blank

hard

Fix the error in the code to properly remove the listener.

Firebase

const ref = firebase.database().ref('tasks');
ref.on('value', snapshot => {
  console.log(snapshot.val());
});

// Remove listener
ref.[1]('value');

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AremoveListener

Bstop

Coff

Dcancel

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'removeListener' or 'stop' causes errors because they don't exist.

Not removing listeners can cause memory leaks.

The off method removes listeners previously attached with on.

4fill in blank

hard

Fill both blanks to read data once and handle errors.

Firebase

firebase.database().ref('profiles').[1]('value').then(snapshot => {
  console.log(snapshot.val());
}).[2](error => {
  console.error(error);
});

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Aonce

Bcatch

Cthen

Don

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'on' instead of 'once' reads data continuously.

Using 'then' instead of 'catch' for error handling is incorrect.

Use once to read data once, and catch to handle errors in the promise.

5fill in blank

hard

Fill all three blanks to listen for child added events and log the new child's key and value.

Firebase

firebase.database().ref('notifications').[1]('child_added', snapshot => {
  const key = snapshot.[2];
  const value = snapshot.[3]();
  console.log(key, value);
});

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

Aon

Bkey

Cval

Donce

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'once' instead of 'on' causes only one event.

Using 'val' without parentheses causes errors.

Accessing 'key' as a method instead of a property causes errors.

Use on to listen continuously, key to get the child's key, and val() to get its value.