Event filtering in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to filter events by their name.

Blockchain / Solidity

const filteredEvents = events.filter(event => event.[1] === 'Transfer');

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

Atype

Btopic

CeventName

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong property name like 'type' or 'topic' which does not hold the event name.

The property name holds the event's name, so filtering by event.name === 'Transfer' selects only Transfer events.

2fill in blank

medium

Complete the code to filter events emitted by a specific address.

Blockchain / Solidity

const filteredEvents = events.filter(event => event.[1] === '0x1234abcd');

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

Asender

Bfrom

Caddress

Demitter

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'address' or 'emitter' which may not be the correct property in the event object.

The from property usually stores the address that emitted the event, so filtering by event.from === '0x1234abcd' selects events from that address.

3fill in blank

hard

Fix the error in the code to filter events with a value greater than 1000.

Blockchain / Solidity

const bigValueEvents = events.filter(event => event.value [1] 1000);

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

A>

B==

C<

D=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' instead of '>' causes syntax or logic errors.

Using '==' checks equality, not greater than.

To filter events where the value is greater than 1000, use the greater than operator >. Using = is an assignment, not a comparison.

4fill in blank

hard

Fill both blanks to filter events with a topic matching '0xabc' and a block number greater than 5000.

Blockchain / Solidity

const filtered = events.filter(event => event.[1] === '0xabc' && event.[2] > 5000);

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Atopic

BblockNumber

Cblock

Dhash

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'block' instead of 'blockNumber' which may not exist.

Using 'hash' which is unrelated to topic or block number.

The topic property holds the event topic, and blockNumber holds the block number. Filtering by these selects events with the given topic and block number above 5000.

5fill in blank

hard

Fill all three blanks to create a dictionary of event counts by event name, filtering only events with value greater than 10.

Blockchain / Solidity

const eventCounts = events.reduce((acc, event) => {
  if (event.[1] > 10) {
    acc[event.[2]] = (acc[event.[3]] || 0) + 1;
  }
  return acc;
}, {});

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

Avalue

Bname

Dtopic

Attempts:

3 left

💡 Hint

Common Mistakes

Using different properties for counting keys causes incorrect counts.

Checking wrong property for value filtering.

We check if event.value is greater than 10, then count events by their name. The accumulator key uses event.name to count occurrences.