Is there a known problem with parsing events containing strings in Truffle/Web3?

I'm using truffle with the following simple contract

contract Board
    string  foo;
    event Shout();
    event TextEvent(
        string  indexed text,
        uint timestamp

    function shout(string _text)

    function getFoo() returns(string){
        return foo;

When I call shout(_) foo is set correctly and a Shout event is triggered and I can listen to this without any problems.

  var board = Board.deployed();
  var shouts=board.Shout();
  shouts.watch(function(error, result){
    if (!error)

However when I watch for TextEvents with the following code

    var board = Board.deployed();
    var textEvent=board.TextEvent();
    textEvent.watch(function(error, result){
        if (!error) console.log("shout",result);

I get the following error which seems to be related to converting bytes32 into a string:

Uncaught BigNumber Error: new BigNumber() not a base 16 number:

So the question is how can you listen to events containing strings in Web3 without running into this error?

  • 1
    This appears to be a bug in web3. I get similar error when trying to return bytes from an event. Please raise an bug report in the following repo - github.com/ethereum/web3.js/issues Mar 16, 2016 at 21:09
  • 2
    Most likely because the parsing function has been passed a string with the "0x" at the beginning like "0x6c3c...". Apr 16, 2016 at 0:23

3 Answers 3


I saw this when my blockchain wasn't fully synced. The contract was expecting a string to be returned, but since that string hadn't been set yet it was returning null, which would blow up on parsing.

I believe the same thing could happen when pointing to an address that doesn't actually implement that API. If the fallback function doesn't return a string then you'll have trouble parsing a string.

Just make sure your blockchain is synced, and you're pointing to the right account.

  • 1
    This should be the accepted answer. This seems to happen if web3 (for example) tries to communicate with a contract which is not locally synced yet.
    – q9f
    Jun 30, 2016 at 20:34
  • 2
    To add. I experienced this bug, because the ABI didn't correctly correspond to the contract. It expected a string, and thus threw an error. Jul 31, 2016 at 21:08
  • 1
    Also I'd like to point out that this can be caused by even slight modifications to the ABI. I got this error when had forgotten to update the client-side ABI so one part of code was expecting indexed fields in events, and the other one was not aware of them. This resulted in the new BigNumber() not a base 16 number error as well. Nov 16, 2018 at 12:38

This is a reproducable bug in web3.js.

ref. https://github.com/ethereum/web3.js/issues/434


From the Github issue:

The BigNumber() is not a base 16 number error can happen in many cases, yet the causes are not necessarily the same. I believe the original post's issue is with using Events that index on "string" types, which I'm running into as well. If my contract event marks a "string" type as "indexed", i get the same error. But if I restrict the "indexed" keyword to only "address" type, I'm fine. I'm trying to find documentation on what data types can be "indexed" in a contract event, but to no avail. My gut feeling is anything that can be parsed as a number (address, integers etc) might be OK. I don't think blockchain synching is the issue here.

So try removing any indexes on string fields in the event definition for now until they fix the bug.

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