A function in my contract when called on the truffle develop command line gives output in BigNumber format. Here is what I wrote on the command line:

instance = contract.at('deployed address')


I tried instance.getAge().toNumber() but that throws an error saying that toNumber isn't defined. I checked How to convert BigNumber to Number in Truffle framework? however that doesnt seem to work on command line.

Similary outputs from functions returning bytes32 are in hex.I checked web3 return bytes32 string but web3.utils.toAscii(x) {x is any variable} throws an error

"Cannot read property toAscii of undefined"

I read the stack related to that and that also didn't help.

1 Answer 1


Contract function calls in Truffle return promises so you have to add a callback to get the response. If getAge() is declared as either constant, pure or view in the Solidity contract you can do instance.getAge().then(age => age.toNumber()) if it doesn't have any of those modifiers then you need to do instance.getAge.call().then(age => age.toNumber())

  • Thanks! I similarly had a function getname()that should return string but yields hex as output. So for that should I type: instance.getname().then(name => web3.toAscii(name)) ? Commented Jan 18, 2018 at 11:28
  • No worries! Also you shouldn't have to convert the string return value of a function from hex. Is getName() declared with either constant, view, or pure after the function name as suggested above? If it isn't then consider adding it. If you can't add it for some reason use instance.getname.call() instead.
    – willjgriff
    Commented Jan 18, 2018 at 12:57
  • Ya it is constant So I did instance.getname().then(name => web3.toAscii(name)) . It did work, however it gave these strings of \u0000 padded after the name. Anyway to remove that? Commented Jan 18, 2018 at 15:46
  • Where do you get the instance from? And does the function in Solidity return a string, eg it looks similar to this function getName() constant returns (string)?
    – willjgriff
    Commented Jan 18, 2018 at 15:58
  • pragma solidity ^0.4.17; contract MyFirst { bytes32 name; function set(bytes32 newName) public { name = newName; } function get() public constant returns (bytes32){ return name; } } I use bytes32 not string, because solidity doesnt function well with strings. It throws weird errors. Commented Jan 18, 2018 at 16:33

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