Steering clear of chained subscribe() functions in RxJs 6

At times, I find myself in need of a value from a previous observable in order to run another function that relies on that value, creating a chain of dependencies. This often results in nested subscribe() calls, making the code messy and hard to manage. Here's an example:

getObservableData().subscribe(next=>
    let dialogRef=this.dialog.open(EvalListComponent, {data: next})
    dialogRef.afterClosed().subscribe(next=>{
        let k=dialogRef.componentInstance.getAnotherObservableData()
            .subscribe( next=> doSomething(next))
}))

What is the best approach for handling such situations? I want to flatten the structure and avoid nested subscriptions. I am aware of the pipe function and its usage with rxjs operators, but how can this be achieved?

Answer №1

If you're looking to level up your understanding of RxJS, I highly recommend checking out this insightful article on flattening strategies in RxJS.

In summary, the key is to familiarize yourself with map operators such as: mergeMap, switchMap, concatMap, exhaustMap.

These operators operate in a similar manner:

  1. They map a value to an observable (you decide what observable to return)

  2. They flatten the returned observable (by subscribing to it)

  3. They implement a strategy before/after flattening ("Flattening Strategy")

Your task is to determine which strategy best suits your use case. This article provides valuable insights to help you make that decision.

Answer №2

Typically, my preference lies in generating the Subject while carrying out the asynchronous task and keeping an eye out for any modifications that may occur.

Take this instance:

private actionUpdateSubject: Subject<string>;

public onActionUpdate(data): void {
    this.actionUpdateSubject.next(data);
}

const subscription = this.actionUpdateSubject
    .pipe(
        distinctUntilChanged()
    )
   .subscribe(update => {});

Answer №3

Consider exploring the functionality of MergeMap and/or SwitchMap for your project. SwitchMap enables you to execute an asynchronous operation, verify its success, and then trigger another async request based on the result.

return fetchDataUsingObservable()
.switchMap(response => {
    let dialogRef = this.dialog.open(EvalListComponent, {data: response})
})
.catch(error => {
    return Observable.of(...)
}
.switchMap(result => {
        ...
})
.catch( ...continue the process...)

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