code: function deltaNone(arg, increment) {
    let newIdx = arg.idx + increment;
  
    if (newIdx >= arg.values.length) {
      newIdx = arg.values.length - 1;
    }
  
    if (newIdx < 0) {
      newIdx = 0;
    }
  
    if (arg.idx !== newIdx) {
      arg.idx = newIdx;
      return true;
    }
  
    return false;
  }
docs: Helper function used to handle next/previous when the loop function is 'none'