如何從超類創建子類的實例？

Question

我正在創建一個類及其子類，我需要在其中調用父類的靜態方法以返回子實例。

class Animal{
  static findOne(){
    // this has to return either an instance of Human
    // or an instance of Dog according to what calls it
    // How can I call new Human() or new Dog() here? 
  }
}

class Human extends Animal{
}

class Dog extends Animal{
}

const human = Human.findOne() //returns a Human instance
const day = Dog.findOne() //returns a Dog instance

Answer 1

調用靜態方法時，它的this值是類對象，即您調用它的子類的構造函數。 所以你可以用new實例化它：

class Animal {
  static findOne() {
    return new this;
  }
}

class Human extends Animal{
}

class Dog extends Animal{
}

const human = Human.findOne() // returns a Human instance
const dog = Dog.findOne() // returns a Dog instance