How to convert string to bytes32 in web3js?

Question

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; 
  }
}

score 46 · Accepted Answer · edited Mar 24 '21 at 12:40

46

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"
 });

edited Mar 24 '21 at 12:40

Siggi

3
1

answered Jul 26 '17 at 21:18

Victor Baranov

2,027
1
17
31

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 05 '17 at 23:59
2

@StanJames I've updated my answer with the code for web3 1.0. Previous one was for web 0.x – Victor Baranov Oct 06 '17 at 16:36
1

How to deal with trailing zeroes? – Shubham Chadokar May 19 '19 at 15:46
3

I'm getting Error: incorrect data length Does this method also make the bytes32 the right length somehow? – Patrick Collins Mar 23 '21 at 00:12
1

@PatrickCollins I'm getting the same. Did you find a fix? – Alex C Apr 11 '21 at 16:40
@PatrickCollins The string must be 32-bytes long. Please fill remaining space with null-characters denoted using \0, or any other character you wish. For example, here is a valid bytes32: web3.utils.asciiToHex("Hello, World! :)\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0") – David Callanan Jun 29 '21 at 10:50
@AlexC See my comment above^ – David Callanan Jun 29 '21 at 10:50

How to convert string to bytes32 in web3js?

1 Answers1

For web3 0.x:

For web3 1.0:

Linked

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