function Cat(){

                  this.climb = function(){

                      alert("我会爬树");

                  }

              }

              var cat  = new Cat();

              cat.climb();

              function Dog(){

                  this.parent = Cat;

                  this.parent.apply(this);//当然也可以传参，

                  this.eat = function(){

                      alert("我会吃");

                  }

              }

              var dog = new Dog();

              console.log(dog)

              dog.climb();