code: function areComparable (a, b) {
    if (typeof a !== 'string' && typeof a !== 'number' && !util.isDate(a) &&
        typeof b !== 'string' && typeof b !== 'number' && !util.isDate(b)) {
      return false;
    }
  
    if (typeof a !== typeof b) { return false; }
  
    return true;
  }
docs: Check that two values are comparable