28

I have a contract with a public variable that's bytes32. If I enter the value 20160528 then it auto converts to bytes32. Is there anyway to convert it back from the nodejs terminal? I've been trying

web3.toAscii(testInstance.Date.call()) 

but it just gives me nonsense. Here is the the test code:

contract test {
  bytes32 public Date;

  function test(bytes32 _date){
      Date=_date; 
  }
}
1
  • Convert back to 20160528 ?
    – Gawey
    Jul 26, 2017 at 6:58

1 Answer 1

41

For web3 0.x:

You need to use web3.fromAscii(val) to write correct bytes32 input to contract.

And you are right, anyone can read it with web3.toAscii(val).

Full web3.js code in terms of your designations:

//sets bytes32
testInstance.test.sendTransaction(web3.fromAscii("20160528"), options);

//gets bytes32
testInstance.Date.call(function(err, val) {
    if  (err) console.log(err);
    console.log(web3.toAscii(val));
    // will print "20160528"
 });

For web3 1.0:

Note: fromAscii has been deprecated

You need to use web3.utils.asciiToHex(val) to write correct bytes32 input to contract.

And you are right, anyone can read it with web3.utils.hexToAscii(val).

Full web3.js code in terms of your designations:

//sets bytes32
testInstance.methods.test(web3.utils.asciiToHex("20160528")).send(options);

//gets bytes32
testInstance.methods.Date().call(function(err, val) {
    if  (err) console.log(err);
    console.log(web3.utils.hexToAscii(val));
    // will print "20160528"
 });
7
  • 2
    I'm getting an error Uncaught (in promise) TypeError: hex.substring is not a function when trying to log val, which seems to be a complex object. Have things changed in web3 recently?
    – Stan James
    Oct 5, 2017 at 23:59
  • 2
    @StanJames I've updated my answer with the code for web3 1.0. Previous one was for web 0.x Oct 6, 2017 at 16:36
  • 1
    How to deal with trailing zeroes? May 19, 2019 at 15:46
  • 3
    I'm getting Error: incorrect data length Does this method also make the bytes32 the right length somehow? Mar 23, 2021 at 0:12
  • 1
    @PatrickCollins I'm getting the same. Did you find a fix?
    – Alex C
    Apr 11, 2021 at 16:40

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