A Solidity event is supposed to emit a boolean. In case of won = true the transaction receipt in web3 logs true as expected, but if won = false the emit logs null instead false. I have no idea why. First I thought it is because of the same variable name, but that is not the cause.

I have this Solidity function which either emits "true" or "false"

event GameResult(bool won);

//My simplified contract
function lottery(uint8 guess) public payable returns(bool){
  uint8 result = 1;
  bool won = false;
  if (guess == result) {
    msg.sender.transfer(msg.value * 2);
    won = true;
  emit GameResult(won);

UPDATE: Here is my web3 function to call the contract (only the relevant part. Full code can be found on Github):

async function play() {
  let headsOrTailsSelection = 1;

  //A test to get the emit values from the contract: true "works", "false" not
  headsOrTails.once('GameResult', function(error, event){ console.log(event.returnValues); });

  returnValue = await headsOrTails.methods.lottery(headsOrTailsSelection).send({ from: account, value: amountToBetWei });

General infos:

  • Currently using Ganache as a local blockchain for development
  • Solidity version: ^0.5.0
  • IDE: VS Code
  • Show your web3 code please. Commented Nov 8, 2019 at 7:27
  • @goodvibration Just added it. Thanks for your help.
    – René K
    Commented Nov 8, 2019 at 13:00
  • can you try to load all past events and see if false appears there? I tried your code in vue app and it's working fine. headsOrTails.events.GameResult( { fromBlock: 0 }, function(error, event) { console.log(event.returnValues); } );
    – Yahya
    Commented Nov 8, 2019 at 15:07
  • @Yahya Same result. The events with true return true, the ones with false return null.
    – René K
    Commented Nov 8, 2019 at 15:57
  • can you please switch to another network? like Rinkeby Ganache is not always good when it comes to the events.
    – Yahya
    Commented Nov 8, 2019 at 16:21

2 Answers 2


For me it works fine on remix. I have run your code as is with no changes on remix and it shows the emitted value as true(Input: 1).

True: when given 1

Also it works prefectly well for false too(Input: 5). False when given 5

So maybe if you gave more information like the version of solidity compiler, IDE you are using and the network the contract is being deployed, then maybe there would be a better shot at understanding the problem.

New here! Any suggestions would be appreciated!!!

  • Hi vteja711, thanks for your support. In Remix I don't have issues either. Just added my web3 code above.
    – René K
    Commented Nov 8, 2019 at 13:02
  • 1
    The problem was related to my outdated version of web3.js. Thanks to you and everyone else for helping.
    – René K
    Commented Nov 8, 2019 at 16:42

The problem was related to my outdated version of web3.js. After updating to V1.2.2 (from 1.0.0-beta.34) the problem was solved. There was a Github issue describing the bug.

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