``` // 定义接口 interface Params{ username: string, password: string, id?:number // 可选属性 } interface Callback{ (result:string, error?:number):void; } // 使用接口 function login(url:string, params: Params, callback: Callback){ callback("获取数据成功"); } // 实现 var params: Params = {username:"aa", password:"aa"}; login("http://www.baidu.com", params, (result:string, error:number){ console.log(result); }); ```