What happens to events when you revert?

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1

Hi there, I’m wondering if an emiited event can be reverted. Some people say an emitted event can change stage, revert can certainly revert all state changes. I am wondering why an event is also a stage change. Conceptualy, there is a subtle difference. Thanks.

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2

Hi @maxareo,

I suggest creating a simple example and testing it to check what happens.

Emitted Events don’t change state on chain.

You can also look at the Solidity documentation to see what you can find: https://docs.soliditylang.org/en/v0.8.3/abi-spec.html?highlight=event%20log#events

I assumed that events aren’t emitted when reverting.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract MyContract {
    event DoneStuff();
    
    function doStuff() public {
        emit DoneStuff();
        
        revert();
    }
}

You may also be interested in: Falsehoods that Ethereum programmers believe

3

Right, the same code gave me different results on my local computer and on Ethereum blockchains. On my computer, nothing happened, the transaction succeeded, and I got no error. Yet, on Rinkeby, the transaction got reverted and no event was emitted, hence no state change except gas fee differences: https://rinkeby.etherscan.io/address/0x02487a4ef6c05eb1b50e05a068787d1586731d48

Hoorey!

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4

An emitted event doesn’t change any observable state in the EVM, but it changes the state of the blockchain, because it stores a new log in every node.

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