RxJS

Question

我想对数组的每个元素执行异步操作并将其结果收集到字典中。我目前的做法是：

let asyncOp = () => Rx.Observable.interval(300).take(1);
let dict = {};

Rx.Observable.from(['a', 'b'])
  .mergeMap(el => asyncOp()
              .map(asyncOpRes => dict[el] = asyncOpRes)
              .do(state => console.log('dict state: ', dict))
  )
  .takeLast(2)
  .take(1)
  .map(() => dict)
  .subscribe(res => console.log('dict result: ', res));

<script src="https://npmcdn.com/@reactivex/rxjs@5.0.0-beta.7/dist/global/Rx.umd.js"></script>

基本上这就像我想要的那样工作，但它似乎是 RxJs 运算符的尴尬用法。所以我需要以下方面的帮助：

避免 dict 突变（尝试使用 scan()，但不知道如何在这里使用它。有一个 mergeScan() 方法，但这里相同）
takeLast 和 take - 的用法应该可以简化吗？

我想我缺少一个 RxJS 运算符来帮助我简化它。

Answer 1

到"execute an async operation on every element of an array and collect its results in a dictionary"可以使用mergeMap and reduce函数显着简化代码：

import * as Rx from "rxjs/Rx";

const asyncOp = () => Rx.Observable.interval(300).take(1);

Rx.Observable.from(["a", "b"])

    // Perform the async operation on the values emitted from the
    // observable and map the emitted value and async result into
    // an object.

    .mergeMap((key) => asyncOp().map((result) => ({ key, result })))

    // Use reduce to build an object containing the emitted values
    // (the keys) and the async results.

    .reduce((acc, value) => { acc[value.key] = value.result; return acc; }, {})
    .subscribe((value) => { console.log(value); });

RxJS - 收集异步操作结果

RxJS - Collect async operation results

javascript

reactive-programming

observable

typescript