code: function isObject(value) {
  
              if (typeof value === 'object' && value !== null &&
                      !(value instanceof Boolean) &&
                      !(value instanceof Date)    &&
                      !(value instanceof Number)  &&
                      !(value instanceof RegExp)  &&
                      !(value instanceof String)) {
  
                  return true;
              }
  
              return false;
          }
docs: used to check, if the value of a property is an object
  (cyclic logic is only needed for objects)
  only needed for cyclic logic