Conversion of inline-assembly to JS

test.js

const keccak256 = require("keccak256");

// `encryptDecrypt` function
function encryptDecrypt(data, key) {
  let length = data.length;
  // let result.length = length;

  for (let i = 0; i < length; i += 32) {
    const hash = keccak256(key.concat(i.toString())).toString("hex");
    let chunk;

    chunk = data.substr(i, 32);
    chunk = getXOR(chunk, hash);

    result += chunk;
  }

  return result;
}

// utility function
function getXOR(s, K) {
  c = "";
  for (i = 0; i < s.length; i++) {
    for (ik = 0; ik < K.length; ik++) {
      c += String.fromCharCode(
        s[i].charCodeAt(0).toString(10) ^ K.charCodeAt(0).toString(10)
      ); // XORing with letter 'K'
    }
  }
  return c;
}