I'm having trouble to pass bytes32 to a solidity function from javascript. It's converting to an incorrect bytes32 in solidity. The javascript is a test, running with truffle v3.3.1 on testRPC v3.0.5.

MyContract {

  event myEvent(bytes32 id);
  function myTran(bytes32 arg) {

When I pass it a string it works (and myEvent emits a correct hex):

myContract.myTran( "0x2a1acd26847576a128e3dba3aa984feafffdf81f7c7b23bdf51e7bec1c15944c");

this works too:

var x = "0x2a1acd26847576a128e3dba3aa984feafffdf81f7c7b23bdf51e7bec1c15944c";
return myContract.myTran(x);

This works but I i receive a different hex value from the myEvent than the passed hex:

 ... tx executed before  ...
    var x = new String( tx.logs[0].args.id );
    console.log(typeof x, x); // output: string 0x2a1acd26847576a128e3dba3aa984feafffdf81f7c7b23bdf51e7bec1c15944c
    return myContract.myTran(x); // executes but the bytes32 in the event is different

2 Answers 2


I've created a independent test case and it turned out the invalid opcodes were caused by something else.

Anyways, the outcome from my tests is that it fails only if I pass as a String object (it accepts it but converts the 0x0.. string into its ascii values).

Passed as String object .valueOf():

var testFoo = "0x341f85f5eca6304166fcfb6f591d49f6019f23fa39be0615e6417da06bf747ce";
var testFooObj = new String(testFoo);
return instance.sendFoo(testFooObj.valueOf());
// returns correct:
// "0x341f85f5eca6304166fcfb6f591d49f6019f23fa39be0615e6417da06bf747ce"

Passed as object:

var testFooObj = new String(testFoo);
return instance.sendFoo(testFooObj);
// returns incorrectly converted:
// "0x2230783334316638356635656361363330343136366663666236663539316434"


pragma solidity ^0.4.11;

contract Bytes32Test {
    bytes32[] public fooStore;

    function getFooStoreLength() constant returns (uint len) {
        return fooStore.length;

    event logFoo(bytes32 foo);
    function sendFoo(bytes32 foo) {

  • Excellent! Well done. Good luck with the rest of your dev cycle.
    – Max
    Jul 6, 2017 at 11:52

Have you tried passing in the string primitive?

var x = new String(tx.logs[0].args.id);
return myContract.myTran(x.valueOf()); 
  • thanks for the tip. with x.valueOf() I get: Error: VM Exception while processing transaction: invalid opcode as well
    – szerte
    Jul 6, 2017 at 7:46
  • I notice that you aren't indexing q in your event myEvent(bytes32 q); And then you are accessing a formatted event result, specifying id with tx.logs[0].args.id. Could you be reading the wrong argument?
    – Max
    Jul 6, 2017 at 9:33

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