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I'm trying to set up an event in Solidity and listen to it from Web3 but I keep getting a null response. Here's my code:

The relevant part of the contract:

event NewUser(string userid);

function createNewUser(string memory _userId) public {
    // creating the user and setting it to a mapping 
    emit NewUser(_userId);
}

The Javascript, from Ethereum's reference:

async function watchEvents(contract) {
    contract.events.allEvents({
       fromBlock: 0
    },function(error, event){ console.log('all events?'); console.log(event); })
  .on('data', function(event){
     console.log(event); // same results as the optional callback above
  })
  .on('changed', function(event){
     // remove event from local database
  })
  .on('error', console.error);
}

Using another javascript function I can see that new users are being created, and the transactions are listed as successful on Ganache. But the watchEvents method keeps printing null.

What am I missing?

  • Are you using websocket provider? Http provider does not support events – Sanjay S B Aug 8 at 6:32
  • @SanjaySB Not even for listing past data?? Anyway no, I didn't know that. Do you know how do I specify websockets in truffle and point it to ganache? If you write it as an answer and it works it'd be great. – Eddy Aug 8 at 7:04
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You can try out web sockets by adding the following in truffle-config.js file.

networks: {
 development: {
      provider: function() {
        return new Web3.providers.WebsocketProvider("ws://localhost:7545");
      },
      network_id: "5777"
    }
...
}

You will have to import Web3.

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