CODEWITHSUNDEEP
javascriptangularrxjsrxjs5
ankitjain11
ankitjain11

Reputation: 253

Wait for a stream before invoking another stream

How do I wait for one stream (say, StreamA) to return non-null value and then invoke StreamB subscribe function. I'm not particularly interested in StreamA's value. In turn, I am trying to get StreamB's value which might have been updated before the StreamA returned non-null value, and might not have any new events.

I tried, pausable, by looking at this: RxJS: How can I do an "if" with Observables?, but unfortunately could not get it to work. This is because, there are no exported class pausable, rxjs v 5.0.0-beta.6.

This is how far, I've come up with, as per the answer.

export class AuthService { userModel: FirebaseListObservable = this.af.database.list(/users); constructor(private af: AngularFire) {

    var user = this.currentAuthor();
    var userStream = user;

    this.af.auth.flatMap((d) => { console.log(d);return this.userModel.publishReplay(1); });

    this.userModel
      .subscribe((data) => {
        var flag = false;
        data.forEach((item) => {
          if (item.$key && item.$key === user.uid) {
            flag = true;
            return;
          }
        });

        if (flag) {
          console.log('hello');
        } else {
          this.userModel.push({
              firstName: user.auth.displayName.substr(0, user.auth.displayName.lastIndexOf(' ')),
              lastName: user.auth.displayName.substr(user.auth.displayName.lastIndexOf(' '), user.auth.displayName.length),
              displayPic: user.auth.photoURL,
              provider: user.provider,
              uid: user.uid
            }
          );
        }
      })
  }
  public currentAuthor():FirebaseAuthState  {
    return this.af.auth.getAuth();
  }

Hope, I can make myself clear. Even I am getting confused now. :p.

I am new to rxjs and reactive programming. And, any help will be appreciated.

And, btw, thanks for stopping by. :)

Upvotes: 0

Views: 146

Answers (1)

user3743222
user3743222

Reputation: 18665

I suppose by plausible you mean pausable? I am not sure what exactly you are trying to achieve here (control flow?). However, if you want streamB value after streamA produces a value, then you can use flatMap.

streamA.flatMapLatest(function (_){return streamB})

That should give you, anytime streamA emits, the values emitted after that time by streamB.

If you want values including the last one B emitted prior to that time, you can use streamBB = streamB.publishReplay(1) and

streamA.flatMapLatest(function (_){return streamBB})

Haven't tested it, so keep me updated if that works.

Upvotes: 1

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