JavaScript class

1. 抽象类

抽象类定义之后不能被实例化，只能被继承，抽象方法定义之后，必须由继承类实现

abstract class Animal {
  name: string;
  constructor(name) {
    this.name = name;
  }

  abstract say():void
}

class Dog extends Animal {
  constructor(name) {
    super(name);
  }

  say(): void {
    console.log('wangwang');
  }
}