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延期延长承诺

deferred promise typescript

Dominykas Mostauskis · 技术社区 · 7 年前

以下实施

export class Deferred<T> extends Promise<T> {                                   
  public _resolveSelf;
  public _rejectSelf;                                                           
  constructor() {
    super(
      (resolve, reject) =>
      {
        this._resolveSelf = resolve
        this._rejectSelf = reject
      }
    )
  }                                                                             
  public resolve(val:T) { this._resolveSelf(val) }
  public reject(reason:any) { this._rejectSelf(reason) }                        
}

投掷 TypeError: _this is undefined

this Typescript playground ,可以看出编译后的javascript很有趣。在第15行中,在声明 _this 其属性已被指定。

2 回复 | 直到 7 年前

Michael Fry 2 年前

export class Deferred<T> implements Promise<T> {

  private _resolveSelf;
  private _rejectSelf;
  private promise: Promise<T>

  constructor() {
    this.promise = new Promise( (resolve, reject) =>
      {
        this._resolveSelf = resolve
        this._rejectSelf = reject

      }
    )
  }

  public then<TResult1 = T, TResult2 = never>(
    onfulfilled?: ((value: T) =>
      TResult1 | PromiseLike<TResult1>) | undefined | null,
    onrejected?: ((reason: any) =>
      TResult2 | PromiseLike<TResult2>) | undefined | null
    ): Promise<TResult1 | TResult2> {
      return this.promise.then(onfulfilled, onrejected)
    }

  public catch<TResult = never>(
    onrejected?: ((reason: any) =>
      TResult | PromiseLike<TResult>) | undefined | null
    ): Promise<T | TResult> {
      return this.promise.catch(onrejected)
    }

  public resolve(val:T) { this._resolveSelf(val) }
  public reject(reason:any) { this._rejectSelf(reason) }

  [Symbol.toStringTag]: 'Promise'

}

then 和 catch 复制粘贴自 Typescript's Promise interface [Symbol.toStringTag] 行也是Typescript认为这是一个承诺所必需的,尽管您只能在编译时发现这一点。

Bergi 7 年前

如何实现延期承诺以延长承诺?

no good reason to use deferreds .

即使在那时,一个延迟的 是一个

function defer() {
    var deferred = {};
    deferred.promise = new Promise(resolve => {
        deferred.resolve = resolve;
    });
    return deferred;
}

可以看出编译后的javascript很有趣。在第15行中,在_声明期间,已经分配了其属性。

是的,就是这样 super 作品:你不能使用 this

你必须写信

export class Deferred<T> extends Promise<T> {
  public resolve: T=>void;
  public reject: any=>void;
  constructor() {
    var resolveSelf, rejectSelf
    super((resolve, reject) => {
      resolveSelf = resolve
      _rejectSelf = reject
    })
    this.resolve = resolveSelf;
    this.reject = rejectSelf;
  }
}