Listening to events on frontend in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to listen to the 'Transfer' event from a smart contract.

Blockchain / Solidity

contract.on('Transfer', (from, to, amount) => {
  console.log('Transfer from', from, 'to', to, 'amount', [1]);
});

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

Aamount

Bto

Cfrom

Devent

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'to' or 'from' instead of 'amount' to log the transfer value.

The 'amount' parameter holds the value transferred in the event. We log it to see the transfer amount.

2fill in blank

medium

Complete the code to stop listening to the 'Approval' event.

Blockchain / Solidity

contract.[1]('Approval');

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

AremoveAllListeners

Bon

Clisten

Demit

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'on' instead of 'removeAllListeners' to stop listening.

To stop listening to an event, we use 'removeAllListeners' with the event name.

3fill in blank

hard

Fix the error in the code to correctly listen to the 'Deposit' event and log the amount.

Blockchain / Solidity

contract.on('Deposit', (user, amount) => {
  console.log('User deposited:', [1]);
});

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

Adeposit

Buser

Cevent

Damount

Attempts:

3 left

💡 Hint

Common Mistakes

Logging 'user' instead of 'amount' for the deposit value.

The 'amount' parameter holds the deposit value, so we log it to show how much was deposited.

4fill in blank

hard

Fill both blanks to create a filter for the 'Transfer' event where the sender is a specific address.

Blockchain / Solidity

const filter = contract.filters.Transfer([1], [2]);

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

A'0x1234567890abcdef1234567890abcdef12345678'

Bnull

C'0xabcdefabcdefabcdefabcdefabcdefabcdefabcd'

Dundefined

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'undefined' or a wrong address in the blanks.

The first blank is the sender address to filter by. The second blank is 'null' to ignore the receiver address.

5fill in blank

hard

Fill all three blanks to listen to the 'Approval' event, filter by owner address, and log the spender and value.

Blockchain / Solidity

const filter = contract.filters.Approval([1], null);

contract.on(filter, (owner, spender, value) => {
  console.log('Spender:', [2], 'Value:', [3]);
});

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

A'0xabcdefabcdefabcdefabcdefabcdefabcdefabcd'

Bspender

Cvalue

D'0x1234567890abcdef1234567890abcdef12345678'

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up owner and spender addresses or logging wrong variables.

The first blank is the owner address to filter by. Then we log the 'spender' and 'value' parameters from the event.