code: function inherits(subClass, superClass) {
              var Empty = function () {};
              Empty.prototype = superClass.prototype;
              var selfPrototype = subClass.prototype;
              var proto = subClass.prototype = new Empty();
  
              Object.keys(selfPrototype).forEach(function (key) {
                  proto[key] = selfPrototype[key];
              });
  
              subClass.prototype.constructor = subClass;
  
              return subClass;
          }
docs: 为类型构造器建立继承关系
  
  @param {Function} subClass 子类构造器
  @param {Function} superClass 父类构造器
  @return {Function}