interface JsonResponse {

  version:number;

  outOfStock?: boolean;

  readonly body: string;

  update: (retryTimes: number) => void;

  update2(retryTimes: number):void

}

interface JsonResponse2 { [key: string]: number }

interface JsonResponse {

  (): string;

  toFn: string

}

const fn: JsonResponse = () => {

  return 'str'

}

fn.toFn = 'content'

// 接口扩展接口

interface X { x: number }

interface Point extends X { y: number }

// Point {x:numer;y:number}

// 也可扩展类型别名，同时可扩展多个

type Y = { y: number }

interface Point2 extends X, Y { z: number }

// Point2 {x:numer;y:number;z:number}

interface Legged {

  numberOfLegs: number;

}

interface Legged {

  numberOfLegs: 123;

}

// 报错，numberOfLegs 必须都为 number

// ======= 在namespace 中也是如此

namespace Animals {

  export interface Legged {

    numberOfLegs: number;

  }

}

namespace Animals {

  export interface Legged {

    numberOfHands: number;

  }

}

// 合并为

namespace Animals {

  export interface Legged {

    numberOfLegs: number;

    numberOfHands: number;

  }

}

interface JsonResponse {

  version: number

}

interface JsonResponse {

  /** In bytes */

  payloadSize: number

}

interface APICall<R> {

  data: R

}

// 使用

interface JsonResponse { content: string };

const api: APICall<JsonResponse> = { data: { content: 'xxx' } }

api.data.content

// 意味着要有 status 属性的类型才能使用

interface APICall<R extends { status: number }> {

  data: R

}

// 使用

interface JsonResponse { content: string, status: number };

const api: APICall<JsonResponse> = { data: { content: 'xxx', status: 200 } }

api.data.status

interface Ruler {

  get size(): number | string

  set size(value: number | string)

}

const ruler:Ruler = {

  size: 123

}

ruler.size = 456

ruler.size = '456'

ruler.size  // 类型为 string

// Error

// ruler.size = false

interface Syncable { sync(): void }

class Account implements Syncable {

  sync() { }

}

// 必须实现 sync 方法