@rhino.fi/client-js/src/lib/stark/calculateFact.js

const { keccak256, encodePacked } = require('web3-utils')

module.exports = (recipient, baseUnitsAmount, tokenAddress, salt) =>
  keccak256(
    encodePacked(
      { t: 'address', v: recipient },
      { t: 'uint256', v: baseUnitsAmount },
      { t: 'address', v: tokenAddress },
      { t: 'uint256', v: salt },
    ),
    // Remove 0x prefix as starkware seems to expect it to be absent.
  )
    .substring(2)