JavaScript implementation of ERC-7201 ("Namespaced Storage Layout") using noble-hashes.

erc-7201.js

// JavaScript implementation of ERC-7201 ("Namespaced Storage Layout") using noble-hashes
// https://ercs.ethereum.org/ERCS/erc-7201

// https://github.com/paulmillr/noble-hashes
// import { keccak_256 } from '@noble/hashes/sha3';
const { keccak_256 } = await import('https://esm.sh/@noble/hashes@1.4.0/esm/sha3.js');

function arrToBigInt(arr) {
  const hex = `0x${[...arr].map(b => b.toString(16).padStart(2, '0')).join('')}`;
  return BigInt(hex);
}

function bigIntToHex(bigInt) {
  const str = bigInt.toString(16);
  return `0x${str.padStart(str.length + (str.length % 2), '0')}`;
}

function bigIntToArr(bigInt) {
  const str = bigInt.toString(16);
  return Uint8Array.from(str.padStart(str.length + (str.length % 2), '0').match(/.{2}/g), v => parseInt(v, 16));
}

// erc7201(id: string) = keccak256(keccak256(id) - 1) & ~0xff
function erc7201(id) {
  const hash = keccak_256(id);
  const minusOne = bigIntToArr(arrToBigInt(hash) - 1n);
  const hash2 = keccak_256(minusOne);
  const result = arrToBigInt(hash2) & ~BigInt(0xff);
  return bigIntToHex(result);
}

function extractCustomStorageLocation(str) {
  const [formulaId, namespaceId] = str.substring(str.indexOf('@custom:storage-location')).split(' ')[1].split(':');
  if (formulaId.trim() === 'erc7201') {
    return erc7201(namespaceId.trim());
  }
  else {
    throw new Error(`Formula ID "${formulaId}" not supported.`);
  }
}

// extractCustomStorageLocation('   /// @custom:storage-location erc7201:example.main ');
// '0x183a6125c38840424c4a85fa12bab2ab606c4b6d0e7cc73c0c06ba5300eab500'