如何在RxJS或Angular2中的Observables中的过滤器中添加订阅？

Question

I'm new to reactive programming, trying to understand the idea here. I got a problem here and it seems solved, but leaving me more questions, one of them is the filter. Here is some code I borrowed from olsn's answer,

function myLoop(item_array) {
    return Observable.from(item_array)
        // if you don't mind the execution-order you can use "mergeMap" instead of "concatMap"
        .concatMap(item => configHardwareMock(item)
            .switchMap(resultId => Observable.interval(500)
                .do(() => console.info("Checking status of: " + resultId))
                .switchMap(() => intervalCheckingStatus(resultId))
                .filter(status => Boolean(status)) // your logic if the status is valid, currently just a boolean-cast
                .take(1) // and complete after 1 value was valid
                .mapTo(item) // map back to "item" so we can notify the subscriber (this is optional I guess and depends on if you want this feature or not)
            )
        );
}

//an example of such boolean from olsn
function intervalCheckingStatus(resultId) {
  if (Math.random() < .4) {
    return Observable.of(false);
  }

  return Observable.of(true);
}

I think I understood some of the tool statements like concatMap , take , from etc. Now it is the .filter(status => Boolean(status)) , so what if I have to put another serious of REST API requests/communication in this boolean function, there can be another subscrible() code in there. Will it break such a filter? In what order the things(events) will run? Is this hardware communication normal, or I should have make it not async (since it is a hardware not that powerful) ?

Answer 1

To answer your question - you cannot put another subscribe() in the filter(). (subscribe will run but will not have any effect on the filter)

If you want to perform another async function (eg REST API call) to determine what values to filter you will need to chain it with a .flatmap() operator.