Ethereum: Ethersjs: check if transaction method in contract emitted event

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Ethereum: Ethers.js – Checking Transaction Methods for Emitting Events

Introduction

In this article, we will examine the importance of verifying that a transaction method in a smart contract raises an event. Specifically, we will focus on the getOwnerAddress function, which emits the OwnerReturned event.

getOwnerAddress Function

The getOwnerAddress function is called when the owner address changes within a contract:

function getOwnerAddress() public view returns (address) {
emit OwnerReturned("Owner");
}

In this example, we emit the OwnerReturned event with a specific message (« Owner »). This means that every time the getOwnerAddress function is called, it will send this event to all contracts and nodes on the blockchain.

Verifying the event emission

To verify that the getOwnerAddress function is emitting the correct events, we can use Ethers.js. Here is an updated version of the contract with a few more checks:

pragma solidity ^ 0,8,0;
import "
import "
contract MyContract {
private ownerAddress;
uint256 public balance = 0;
event OwnerReturned(String memory address);
function getOwnerAddress() public view returns (address) {
require(msg.sender == ownerAddress, "Only the owner of the contract can call this function");
emit OwnerReturned("Owner");
returnAddress(0); // Returns null to indicate that no new owner was set
}
function setOwner(address _newOwner) public {
require(_newOwner != ownerAddress && !balance, "Cannot change owner or transfer tokens");
ownerAddress = _newOwner;
emit OwnerReturned("Owner");
balance = 0;
}
}

Explanation

In this updated contract:

• We added a `require'' statement to check if the caller is the owner of the contract.

• When setting the owner, we update theownerAddressvariable and raise anOwnerReturnedevent with the message ("Owner").

• In the constructor, we call thesetOwner` function and immediately return without updating the balance.

Conclusion

Verifying that the transaction method emits events is crucial to ensuring the security and integrity of the contract. By using Ethers.js to check event emission, you can catch any potential issues before deploying your contracts to production. This example shows how to write more robust smart contracts by validating event emission and properly handling edge cases.

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