Code Wars: Reverse or rotate?

The input is a string str of digits. Cut the string into chunks (a chunk here is a substring of the initial string) of size sz (ignore the last chunk if its size is less than sz).
If a chunk represents an integer such as the sum of the cubes of its digits is divisible by 2, reverse that chunk; otherwise rotate it to the left by one position. Put together these modified chunks and return the result as a string.
If
  • sz is <= 0 or if str is empty return ""
  • sz is greater (>) than the length of str it is impossible to take a chunk of size sz hence return "".


function revrot(str, sz) {
  
  if (sz <= 0 || str === "" || sz > str.length) {
    return "";
  } 
  
  let arr1 = str.split('').map(item => parseInt(item));
  let arr2 = [];
  let sumUp = function add(a, b) {
    return a + b;
  }
  console.log(arr1);
  while (arr1.length >= sz) {
      arr2.push(arr1.splice(0, sz))
  }
  for (i = 0; i < arr2.length; i++) {
    if ( arr2[i].reduce(sumUp) % 2 === 0) {
      arr2[i].reverse();
    }
    else {
      let goLeft = arr2[i].shift();
      arr2[i].push(goLeft);
    }
  }
  return arr2.map(item => item.join('')).join('');
}

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