SOURCE

class  Animal {
    constructor(name) {
        this.name = name;
    }
    sleep(){
    console.log(this.name + '正在睡觉！');
    }
}
class Cat extends Animal {
    constructor(name, food) {
        super(name);
        this.food = food;
    }
}

let cat = new Cat('小黑', 'fish');
console.log(cat);