To simplify my question, let's say I have a Test.sol with a function that simply output the input:

function testFunc(uint256 value) public pure returns (uint256) {
  return value;

Now I want to test it in truffle

it('uint input test', async () => {
  var test = await Test.deployed()
  res = await test.testFunc.call(0x10000000000000000000000000000001)
  assert.equal(res, 0x10000000000000000000000000000001, 'wrong')

I'm expecting the result should be same as the input, but it fails the assert. Outputs:

BigNumber { s: 1, e: 37, c: [ 2126764793, 25586540000000 ] }

So 0x10000000000000000000000000000001 is changed to 0x1000000000000001d172c5f60ac00000, I assume it's the JavaScript number overflow problem?

It causes problem when I try to test the bit operations, such as checking ERC721 token ID. How can I bypass it?

  • 1
    The problem is javascript numbers do not have enough precision. Either compare them as BigNumers (the objects returned by web3js), or transform them into strings and compare the as such.
    – Ismael
    Commented Jul 24, 2018 at 3:36

1 Answer 1


While this may not be an exact answer, it works when using chai promise:



const res = await test.testFunc.call(0x10000000000000000000000000000001)

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