Fast cartesian product JS

cartesian.js

function cartesian() {
  const N = arguments.length;

  var arr_lengths = Array(N);
  var digits = Array(N);
  var num_tot = 1;
  for (var i = 0; i < N; ++i) {
    const len = arguments[i].length;
    if (!len) {
      num_tot = 0;
      break;
    }
    digits[i] = 0;
    num_tot *= (arr_lengths[i] = len);
  }

  var ret = Array(num_tot);
  for (var num = 0; num < num_tot; ++num) {

    var item = Array(N);
    for (var j = 0; j < N; ++j) { item[j] = arguments[j][digits[j]]; }
    ret[num] = item;

    for (var idx = 0; idx < N; ++idx) {
      if (digits[idx] == arr_lengths[idx] - 1) {
        digits[idx] = 0;
      } else {
        digits[idx] += 1;
        break;
      }
    }
  }
  return ret;
}