2

Here is a very small repo to show the issue: https://github.com/adamdry/ethers-event-issue

But I'll explain it here too. This is my contract:

//SPDX-License-Identifier: UNLICENSED;
pragma solidity 0.8.4;

contract ContractA {

    event TokensMinted(uint amount);

    function mint(uint amount) public {
        emit TokensMinted(amount);
    }

}

And this is my test code:

import * as chai from 'chai'
import { BigNumber, ContractTransaction } from 'ethers'
import { ethers } from 'hardhat'
import { ContractA, ContractAFactory } from '../typechain'

const expect = chai.expect

describe("Example test", function () {
    it("should fire the event", async function () {
        const [owner] = await ethers.getSigners();

        const contractAFactory = (await ethers.getContractFactory(
            'ContractA',
            owner,
        )) as ContractAFactory

        const contractA: ContractA = await contractAFactory.deploy()

        contractA.on('TokensMinted', (amount: BigNumber) => {
            // THIS LINE NEVER GETS HIT
            console.log('###########')
        })

        const contractTx: ContractTransaction = await contractA.mint(123)
        const contractReceipt: ContractReceipt = await contractTx.wait()

        for (const event of contractReceipt.events!) {
            console.log(JSON.stringify(event))
        }
    });
});

I was expecting the ########### to get printed to the console however it doesn't so the listener function isn't being executed for some reason.

If I dig into the ContractReceipt the correct event data is there:

{
  "transactionIndex": 0,
  "blockNumber": 2,
  "transactionHash": "0x55d118548c8200e5e6c19759d9aab56cb2e6a274186a92643de776d617d51e1a",
  "address": "0x5FbDB2315678afecb367f032d93F642f64180aa3",
  "topics": [
    "0x772f66a00a405709c30e7f18feadcc8f123b20c09c7260165d3eec36c9f21372"
  ],
  "data": "0x000000000000000000000000000000000000000000000000000000000000007b",
  "logIndex": 0,
  "blockHash": "0x808e6949118509b5a9e482e84cf47921a2fcffbcd943ebbd8ce4f6671469ee01",
  "args": [
    {
      "type": "BigNumber",
      "hex": "0x7b"
    }
  ],
  "event": "TokensMinted",
  "eventSignature": "TokensMinted(uint256)"
}

1 Answer 1

1

The problem here is, default polling interval in an ethers provider is 4 seconds. By the time it polls, your it('', async function () {}) has finished execution, and garbage collector might even clear the local variables contract immediately after it finishes.

A simple solution could be to add a wait of 4 seconds or higher, v

  ...

  for (const event of contractReceipt.events!) {
    console.log(JSON.stringify(event))
  }

  // waits for 5 sec
  await new Promise(res => setTimeout(res, 5000));
});

You can also reduce the polling interval, however, the minimum value is 1 msec.

contractA.provider.pollingInterval = 1;

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