A short while ago, I found a fantastic Medium article explaining Smart Contract storage.

The examples in this article have helped me to understand how to read a Smart Contract's storage values from the command line / console.

However, with the version 1.0.0 of web3js going into Beta - and the NPM version of web3js being installed by default being the 1.0.0 Beta version, I thought that I would upgrade my code using the information from the aforementioned article to the new library.

The problem is that I can't replicate the same behavior of web3.sha3 using the new version of the library; web3Utils.sha3.

To clarify, here are some examples - starting with the output that I get from the stable, but pre-V1.0.0 web3.sha3 function and then from the new, Beta version of the web3js library:

To give you some context, the test is based on accessing the mappings data in this contrived Smart Contract:

pragma solidity ^0.4.0;

contract StorageTest {
    mapping(address => uint256) public storedData;

    function addDataToMapping(address account, uint256 amount) public {
        storedData[account] = amount;

The way that I determine how to access the mapping's data for the address 0x90F8bf6A479f320ead074411a4B0e7944Ea8c9C1 is by using the following pre-V1.0.0 web3js call:

web3.sha3("00000000000000000000000x90F8bf6A479f320ead074411a4B0e7944Ea8c9C10000000000000000000000000000000000000000000000000000000000000000", {"encoding":"hex"})

This results in the hash value


Now, if we simply port this over to the V1.0.0 library then the code looks like this:

web3Utils.sha3("00000000000000000000000x90F8bf6A479f320ead074411a4B0e7944Ea8c9C10000000000000000000000000000000000000000000000000000000000000000", {"encoding":"hex"})   

However, this results in the following (different) hash being output:


I tried removing the {"encoding":"hex"} parameter (because this isn't mentioned in the documentation:


But unfortunately, I still get the same output:


The documentation mentions a web3Utils.soliditySha3 function that sounded like it might do the trick, so I switched this function call in instead:

web3Utils.soliditySha3("00000000000000000000000x90F8bf6A479f320ead074411a4B0e7944Ea8c9C10000000000000000000000000000000000000000000000000000000000000000", {"encoding":"hex"})

This time I got a different value, but it is not the one that I am looking for:


I also tried removing the {"encoding":"hex"} parameter (because this also isn't mentioned in the documentation:


But this just results in the same, incorrect, value as the web3Utils.sha3 function calls:


I have also tried various permutations of the "Any type, or an object with {type: 'uint', value: '123456'}" parameter format:

web3Utils.soliditySha3({type: 'string', value: "00000000000000000000000x90F8bf6A479f320ead074411a4B0e7944Ea8c9C10000000000000000000000000000000000000000000000000000000000000000"})

And yet I still can't get the correct value.

Does anyone know how to correctly address a mapping or struct storage address using the latest web3js library functions?

1 Answer 1


Removing the extra 'x' in the key and prefixing with '0x' it returns the same value in

const Web3 = require('web3')
const web3 = new Web3();

const index = "0000000000000000000000000000000000000000000000000000000000000000"
const key =   "00000000000000000000000090F8bf6A479f320ead074411a4B0e7944Ea8c9C1";
const newKey =  web3.utils.sha3("0x" + key + index)


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.