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

Practice - 5 Tasks

1fill in blank

easy

Complete the code to listen for the 'Transfer' event on a contract.

Blockchain / Solidity

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

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

ATransfer

BApproval

CDeposit

DWithdraw

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong event name like 'Approval' instead of 'Transfer'.

Forgetting to put the event name as a string.

The event name to listen for is 'Transfer'. This matches the event emitted by the contract.

2fill in blank

medium

Complete the code to remove the event listener for 'Transfer'.

Blockchain / Solidity

contract.[1]('Transfer', callbackFunction);

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

Alisten

Boff

CremoveListener

Dstop

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'off' which may not be supported in some libraries.

Using 'listen' which is not a valid method.

To remove a specific event listener, use removeListener with the event name and callback.

3fill in blank

hard

Fix the error in the code to correctly listen for events with filters.

Blockchain / Solidity

const filter = contract.filters.[1](null, userAddress);
contract.on(filter, (from, to, amount) => {
  console.log(`Filtered transfer from ${from} to ${to} of ${amount}`);
});

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

AApproval

BTransfer

CDeposit

DWithdraw

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong event name in the filter.

Passing incorrect parameters to the filter method.

The filter should be created for the 'Transfer' event to listen for transfers involving the user address.

4fill in blank

hard

Fill both blanks to create a filter for 'Approval' events where the owner is a specific address.

Blockchain / Solidity

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

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

AApproval

B0x1234567890abcdef1234567890abcdef12345678

CTransfer

D0xabcdefabcdefabcdefabcdefabcdefabcdefabcd

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Transfer' instead of 'Approval' for the event name.

Using the wrong address or null in the filter parameters.

The filter is for 'Approval' events where the first parameter (owner) matches the given address.

5fill in blank

hard

Fill all three blanks to listen for 'Deposit' events and log the depositor and amount.

Blockchain / Solidity

contract.on('[1]', ([2], [3]) => {
  console.log(`Deposit by ${depositor} of ${amount}`);
});

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

ADeposit

Bdepositor

Camount

Dwithdrawer

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong event name like 'Withdraw'.

Using incorrect parameter names that don't match the event.

The event name is 'Deposit'. The callback parameters are 'depositor' and 'amount' to match the event signature.