4、类（class）

类（Class）：定义了一切事务的抽象特点
对象（Object）：类的实例
面向对象（OOP）三大特性：封装、继承、多态

class Animal {
  name: string;
  constructor(name: string) {
    this.name = name
  }
  run() {
    return `${this.name} is running`
  }
}
const snake = new Animal('lily')
console.log(snake.run())
class Dog extends Animal {
  bark() {
    return `${this.name} is barking`
  }
}
const xiaobao = new Dog('xiaobao')
console.log(xiaobao.bark())
class Cat extends Animal {
  constructor(name) {
    super(name)
  }
  run() {
    return 'Meow,' + super.run()
  }
}
const kitty = new Cat('kitty')
console.log(kitty.run())