Emitting events in Blockchain / Solidity - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of emitting events in blockchain smart contracts?

Emitting events allows smart contracts to log information that external applications can listen to and react upon. It helps track contract activity without storing data on-chain.

beginner

How do you declare an event in Solidity?

You declare an event using the event keyword followed by the event name and parameters, for example: event Transfer(address indexed from, address indexed to, uint256 amount);

intermediate

What does the indexed keyword do in event parameters?

The indexed keyword marks parameters that can be used as filters when searching for events. Up to 3 parameters can be indexed to make event queries efficient.

beginner

How do you emit an event inside a Solidity function?

You use the emit keyword followed by the event name and arguments, like: emit Transfer(msg.sender, recipient, amount);

intermediate

Why are events cheaper than storing data on the blockchain?

Events store data in transaction logs, which are cheaper to write and do not consume as much gas as storing data in contract storage. However, event data is not accessible by contracts, only by external listeners.

Which keyword is used to declare an event in Solidity?

A emit

B event

C log

D notify

The event keyword declares an event. The emit keyword is used to trigger it.

What does the emit keyword do in Solidity?

A Declares a new event

B Filters events

C Deletes an event

D Triggers an event to be logged

The emit keyword triggers an event so it is recorded in the transaction logs.

How many parameters can be indexed in a Solidity event for filtering?

A 3

B 2

C 1

D Unlimited

Up to 3 parameters can be marked indexed to allow efficient filtering.

Where is event data stored in the blockchain?

A In transaction logs

B In contract storage

C In the blockchain header

D In the contract code

Event data is stored in transaction logs, which are cheaper and accessible off-chain.

Can smart contracts read event data after it is emitted?

A Yes, directly

B Only if indexed

C No, only external apps can read it

D Yes, but only in the same transaction

Contracts cannot access event data; only external applications can listen and read events.

Explain how emitting events helps external applications interact with smart contracts.

Think about how apps watch for changes without reading contract storage.

Describe the syntax and usage of declaring and emitting an event in Solidity.

Focus on how to define and then trigger an event.