Operators within an observable that perform actions after a specific duration has elapsed

Question

Operators within an observable that perform actions after a specific duration has elapsed

Is there a way in an rxjs observable chain to perform a task with access to the current value of the observable after a specific time interval has elapsed? I'm essentially looking for a functionality akin to the tap operator, but one that triggers only if a certain amount of time passes without any new values emitted by the observable. In essence, it's like a combination of tap and timeout.

Here's a hypothetical scenario:

observable$.pipe(
  first(x => x > 5),
  tapAfterTime(2000, x => console.log(x)),
  map(x => x + 1)
).subscribe(...);

This example is fabricated, and the "tapAfterTime" function doesn't actually exist. However, the concept revolves around the idea that if 2000ms go by after subscribing to the observable without encountering a value greater than 5, then execute the tapAfterTime callback function on the current value of the observable. If a value greater than 5 is received before the 2000ms mark, the tapAfterTime callback won't trigger, but the map function will proceed as planned.

Does anyone know of an operator or combination of operators that could achieve this behavior?

javascript angular typescript rxjs rxjs-pipeable-operators

Answer 1

Answer №1

Perhaps this concept is a bit complex, but it may be worth exploring.

The approach involves creating two distinct observables by transforming the source observable$ and then merging them together.

The first Observable, referred to as obsFilterAndMapped, is where filtering and mapping occur.

The second Observable, known as obsTapDelay, triggers a new timer with a specified delay each time the first Observable (obsFilterAndMapped) emits a value. If the delayTime is exceeded before a new value is emitted, the tapAfterTime action is executed. Otherwise, a new timer is set for the next emissions.

Here is the code implementing this concept:

const stop = new Subject<any>();
const obsShared = observable$.pipe(
    finalize(() => {
        console.log('STOP');
        stop.next();
        stop.complete()
    }),
    share()
);
const delayTime = 300;
const tapAfterTime = (value) => {
    console.log('tap with delay', value)
}; 

let valueEmitted;

const obsFilterAndMapped = obsShared.pipe(
    tap(val => valueEmitted = val),
    filter(i => i > 7),
    map(val => val + ' mapped')
);

const startTimer = merge(of('START'), obsFilterAndMapped);

const obsTapDelay = startTimer.pipe(
    switchMap(val => timer(delayTime).pipe(
        tap(() => tapAfterTime(valueEmitted)),
        switchMap(() => empty()),
    )),
    takeUntil(stop),
)

merge(obsFilterAndMapped, obsTapDelay)
.subscribe(console.log, null, () => console.log('completed'))

By using this method, you can perform the tapAfterTime action whenever the source observable$ does not emit any value for longer than the delayTime duration. This functionality applies throughout the lifecycle of observable$.

You can test the code with the following input:

const obs1 = interval(100).pipe(
    take(10),
);
const obs2 = timer(2000, 100).pipe(
    take(10),
    map(val => val + 200),
);
const observable$ = merge(obs1, obs2);

Further improvements could involve encapsulating the global variable valueEmitted within a closure, although this may add complexity to the code without significant benefits.

Answer 2

Perhaps this concept is a bit complex, but it may be worth exploring.

The approach involves creating two distinct observables by transforming the source observable$ and then merging them together.

The first Observable, referred to as obsFilterAndMapped, is where filtering and mapping occur.

The second Observable, known as obsTapDelay, triggers a new timer with a specified delay each time the first Observable (obsFilterAndMapped) emits a value. If the delayTime is exceeded before a new value is emitted, the tapAfterTime action is executed. Otherwise, a new timer is set for the next emissions.

Here is the code implementing this concept:

const stop = new Subject<any>();
const obsShared = observable$.pipe(
    finalize(() => {
        console.log('STOP');
        stop.next();
        stop.complete()
    }),
    share()
);
const delayTime = 300;
const tapAfterTime = (value) => {
    console.log('tap with delay', value)
}; 

let valueEmitted;

const obsFilterAndMapped = obsShared.pipe(
    tap(val => valueEmitted = val),
    filter(i => i > 7),
    map(val => val + ' mapped')
);

const startTimer = merge(of('START'), obsFilterAndMapped);

const obsTapDelay = startTimer.pipe(
    switchMap(val => timer(delayTime).pipe(
        tap(() => tapAfterTime(valueEmitted)),
        switchMap(() => empty()),
    )),
    takeUntil(stop),
)

merge(obsFilterAndMapped, obsTapDelay)
.subscribe(console.log, null, () => console.log('completed'))

By using this method, you can perform the tapAfterTime action whenever the source observable$ does not emit any value for longer than the delayTime duration. This functionality applies throughout the lifecycle of observable$.

You can test the code with the following input:

const obs1 = interval(100).pipe(
    take(10),
);
const obs2 = timer(2000, 100).pipe(
    take(10),
    map(val => val + 200),
);
const observable$ = merge(obs1, obs2);

Further improvements could involve encapsulating the global variable valueEmitted within a closure, although this may add complexity to the code without significant benefits.

Answer 3

Answer №2

Explore the following resources:

Consider implementing something similar to the code snippet below

--

initiateTimer() {
    if (this.timerSub) {
        this.timerSub.unsubscribe();
    }

    this.timerSub = Rx.Observable.timer(2000)
        .take(1)
        .subscribe(this.showPopup.bind(this));
}

Answer 4

Explore the following resources:

Consider implementing something similar to the code snippet below

--

initiateTimer() {
    if (this.timerSub) {
        this.timerSub.unsubscribe();
    }

    this.timerSub = Rx.Observable.timer(2000)
        .take(1)
        .subscribe(this.showPopup.bind(this));
}

Answer 5

Answer №3

Here's an example of how it could look:

let timeout;
observable$.pipe(
  tap((x)=>timeout=setTimeout(()=>console.log(x), 2000)),
   filter(x => x > 5),
   tap(x => clearTimeout(timeout)),
   map(x => x + 1)
);

Answer 6

Here's an example of how it could look:

let timeout;
observable$.pipe(
  tap((x)=>timeout=setTimeout(()=>console.log(x), 2000)),
   filter(x => x > 5),
   tap(x => clearTimeout(timeout)),
   map(x => x + 1)
);

Operators within an observable that perform actions after a specific duration has elapsed

Answer №1

Answer №2

Answer №3

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