RxJS 根据发出的值重复 [英] RxJS repeat depending on emitted value

问题描述

我正在尝试根据 condition 字段中返回的值repeat 一个承诺调用.以下块不起作用，因为 v 未定义并随机抛出 TypeError: Cannot read property 'condition' of undefined

I am trying to repeat a promise call depending on the value returned in condition field. The following block doesn't work because v is undefined and randomly throws TypeError: Cannot read property 'condition' of undefined

console.log 的 o/p 是 { Items: [ 1, 2, 3, 4, 5 ], condition: 5, time: 1513827310333 }

the o/p of console.log is { Items: [ 1, 2, 3, 4, 5 ], condition: 5, time: 1513827310333 }

JSFiddle

const source = Rx.Observable.fromPromise(
  Promise.resolve({
    Items: [1, 2, 3, 4, 5],
    condition: Math.floor(Math.random() * 10),
    time: +new Date()
  })
);

source
  .map(val => val)
  .repeatWhen(val => {
    return val.map(v => { // v is undefined
      if (v.condition > 0) {
        return Rx.Observable.of(v);
      } else {
        return Rx.Observable.empty();
      }
    });
  })
  .finally(() => {
    done();
  })
  .subscribe(val => console.log(val));

推荐答案

让它与外部标志一起工作，并且每次重复都会评估源.

Got it working with an external flag an the source is evaluated for every repetition.

const source = Rx.Observable.defer(() =>
  Promise.resolve({
    Items: [1, 2, 3, 4, 5],
    condition: Math.floor(Math.random() * 10),
    time: +new Date()
  })
);

let condition = false;

source
  .repeatWhen(notifications => {
    return notifications
      .scan(() => {
        return condition;
      }, false)
      .delay(100)
      .takeWhile(() => {
        return condition;
      });
  })
  .do(x => (condition = x.condition !== 0))
  .finally(console.log("done"))
  .subscribe(console.log);

.as-console-wrapper { max-height: 100% !important; top: 0; }

<script src="https://cdnjs.cloudflare.com/ajax/libs/rxjs/5.5.5/Rx.min.js"></script>

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