Event-driven architecture patterns in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to emit an event named 'Transfer' in a smart contract.

Blockchain / Solidity

emit [1](msg.sender, recipient, amount);

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

ATransfer

BSend

CNotify

DEvent

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong event name causes a compilation error.

The event name must match the declared event 'Transfer' to emit it correctly.

2fill in blank

medium

Complete the code to listen for the 'Approval' event in a blockchain client.

Blockchain / Solidity

contractInstance.events.[1]({}, (error, event) => { console.log(event); });

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

ADeposit

BTransfer

CApproval

DWithdraw

Attempts:

3 left

💡 Hint

Common Mistakes

Listening to a wrong event name results in no events captured.

The event listener must use the exact event name 'Approval' to capture those events.

3fill in blank

hard

Fix the error in the event filter to only get events where 'from' equals the sender address.

Blockchain / Solidity

contractInstance.getPastEvents('Transfer', { filter: { [1]: senderAddress } });

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

Aamount

Bfrom

Cto

Drecipient

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'to' or 'recipient' filters the wrong address field.

The filter key must be 'from' to filter events by sender address.

4fill in blank

hard

Fill both blanks to create a subscription that listens for 'Deposit' events and logs the amount.

Blockchain / Solidity

subscription = contract.events.[1]().on('[2]', (event) => { console.log(event.returnValues.amount); });

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

ADeposit

BTransfer

Cdata

Dchanged

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong event name or event type causes no logs.

The subscription listens for 'Deposit' events and the event type to listen for is 'data' to receive event data.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps event names to their handler functions if the event name starts with 'On'.

Blockchain / Solidity

handlers = { [1]: [2] for [3] in eventList if [1].startswith('On') }

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

Aevent

Bhandle_event

Dhandler

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing variable names or using wrong function names.

The comprehension uses 'event' as key and 'handle_event' as value for each 'event' in eventList starting with 'On'.