接口仅约束结构，不要求实现，

    1. // 接口中只需定义结构，不需要初始化
    2. interface Person {
    3.   firstName: string;
    4.   lastName: string;
    5. }
    6. // greeting函数通过Person接口约束参数解构
    7. function greeting(person: Person): void {
    8.   console.log("Hello, " + person.firstName + " " + person.lastName);
    9. }
    10. greeting({ firstName: "Jane", lastName: "Eye" }); // 正确
    11. greeting({ firstName: "Jane" }); // 错误