Javascript类，继承

Question

我需要一些关于以下代码行的帮助：

class Race{
        constructor(_raceName){
            this.raceName = _raceName;
        }
    }

class Animal extends Race{
        constructor(_raceName, _animal) {
            super(_raceName, _animal);
            this.animal = _animal;
        
        }
    }

class Pet extends Animal{
        constructor(_petName, _Birthday, _animal){
            super(_animal)
            this.petName = _petName;
            this.Birthday = _Birthday;
        }
    
    }

var Pet1 = new Pet("Pluto", "2000/10/01", "Mamals")
console.log(Pet1)

当我在终端中运行它时，我得到以下结果:宠物{ raceName：‘哺乳动物’，动物:未定义，petName：‘冥王星’，生日：'2000/

为什么我的动物没有定义？我希望在那里有“狗”这个字符串

Answer 1

你的Animal类需要2个参数，所以如果你只发送一个参数，它将使第二个参数成为undefined。您可以设置一个默认值，如果没有输入任何值，则将其设置为非undefined。

​

class Race{
        constructor(_raceName){
            this.raceName = _raceName;
        }
    }

class Animal extends Race{
        constructor(_raceName, _animal="dog") {
            super(_raceName, _animal);
            this.animal = _animal;
        
        }
    }

class Pet extends Animal{
        constructor(_petName, _Birthday, _animal){
            super(_animal)
            this.petName = _petName;
            this.Birthday = _Birthday;
        }
    
    }

var Pet1 = new Pet("Pluto", "2000/10/01", "Mamals")
console.log(Pet1)

​

而且，您必须更改您的宠物类，如下所示，才能使其正确。默认情况下，它将接受"dog"，你可以根据你的实现来输入你的动物类。

​

class Race{
        constructor(_raceName){
            this.raceName = _raceName;
        }
    }

class Animal extends Race{
        constructor(_raceName, _animal="dog") {
            super(_raceName, _animal);
            this.animal = _animal;
        
        }
    }

class Pet extends Animal{
        constructor(_petName,_animalClass, _Birthday, _animal){
            super(_animal,_animalClass)
            this.petName = _petName;
            this.Birthday = _Birthday;
        }
    
    }

var Pet1 = new Pet("Pluto","cat", "2000/10/01", "Mamals")
console.log(Pet1)

​

Answer 2

我想您需要添加一个额外的类来定义实例是一条狗。

​

class Race{
        constructor(_raceName){
            this.raceName = _raceName;
        }
    }

class Animal extends Race{
        constructor(race, _animal) {
            super(race);
            this.animal = _animal;
        }
    }

class Pet extends Animal{
        constructor(_petName, _Birthday, race, _animal){
            super(race, _animal);
            this.petName = _petName;
            this.Birthday = _Birthday;
        }
    }
    
class Dog extends Pet {
  constructor(...params) {
    super(...params, "dog");
  }
}

var Pet1 = new Dog("Pluto", "2000/10/01", "Mamals")
console.log(Pet1)

​