设计模式在 TypeScript 中的应用

定义

代理模式是为一个对象提供一个代用品，或占位符，以便控制对它的访问。

实现

思路：把客户端真正调用的类和方法隐藏，只暴露代理类给客户端。

简单点的例子：

// 食品服务接口interface FootService {  makeChicken (salt: string): void;  makeNoodle (salt: string): void}// 食物接口class Foot {  // 种类  public type: string  // 重量  public salt: string  public constructor (type: string, salt: string) {    this.type = type    this.salt = salt    this.cook()  }  // cook  public cook (): void {    console.log(`种类：${this.type}，重量：${this.salt}`)  }}// 真实的食品服务class FootServiceReal implements FootService {  public chicken: Foot  public Noodle: Foot  public makeChicken (salt: string): any {    this.chicken = new Foot('chicken', salt)  }  public makeNoodle (salt: string): any {    this.Noodle = new Foot('noodle', salt)  }}// 代理食品服务class FootServiceProxy implements FootService {  // 真实的实现类  private footServiceReal: FootServiceReal  private prepareFood () {    if (!this.footServiceReal) {      this.footServiceReal = new FootServiceReal()    }  }  public makeChicken () {    console.log('马上开始做鸡肉')    console.log('==========')    this.prepareFood()    this.footServiceReal.makeChicken('500g')    console.log('==========')    console.log('鸡肉做好了')  }  public makeNoodle () {    console.log('马上开始做面条')    console.log('==========')    this.prepareFood()    this.footServiceReal.makeNoodle('100g')    console.log('==========')    console.log('面条做好了')  }}const foot = new FootServiceProxy()foot.makeChicken()console.log('========')foot.makeNoodle()

缓存代理比较常见，可以为一些开销比较大的运算结果提供缓存，在下次运算时，如果传递进来的参数跟以前一致，则可以直接返回前面存储的运算结果。

// 加法function add (arg: Array<number>): number {  console.log('进行一次加法计算')  return arg.reduce((prev: number, cur: number): number => prev + cur, 0)}// 乘法function mul (arg: Array<number>): number {  console.log('进行一次乘法计算')  return arg.reduce((prev: number, cur: number): number => prev * cur, 1)}// 代理class CalculateProxy {  private cache: Object = {}  private fn: Function  public constructor (fn: Function) {    this.fn = fn  }  public calculate (...arg: Array<number>): void {    const str: string = arg.join(',')    if (str in this.cache) {      return this.cache[str]    } else {      return this.cache[str] = this.fn(arg)    }  }}const addCalculateProxy = new CalculateProxy(add)console.log(addCalculateProxy.calculate(1, 2, 3, 4))console.log(addCalculateProxy.calculate(1, 2, 3, 4))console.log('=========')const mulCalculateProxy = new CalculateProxy(mul)console.log(mulCalculateProxy.calculate(1, 2, 3, 4))console.log(mulCalculateProxy.calculate(1, 2, 3, 4))