1. interface Animal{
    2.   name: string;
    3.   age: number
    4. }
    6. interface Dog extends Animal{
    7.   eat(str: string): void;
    8. }
    10. class wolfDog implements Dog {
    11.   name: string;
    12.   age: number;
    13.   eat(str: string): void {
    14.       console.log(str);
    15.   }
    16.   constructor(name: string, age: number) {
    17.     this.name = name;
    18.     this.age = age;
    19.   }
    20. }
    22. let w: wolfDog = new wolfDog('狗', 18);