I am working on setting up a ReplaySubject in my Angular application, and I want to configure it so that there is always a delay between when an Observer subscribes to it and when it receives an update.
let delayedReplay = new ReplaySubject(1);
delayedReplay.subscribe((data) => {
console.log('Got:', data);
});
delayedReplay.next('Test');
My goal is to add a delay to the ReplaySubject itself so that the code above would display 'Got: Test' after, for example, 1 second.
To achieve the desired outcome, you have to connect the Subject with delay and then utilize the resulting Observable for subscription purposes, all while still utilizing the original Subject for emitting values.
The code implementation is as follows:
let replay = new ReplaySubject(1);
let delayedReplay = replay.pipe(delay(1000));
delayedReplay.subscribe((data) => {
console.log('Got:', data);
});
replay.next('Test');
This approach should function effectively in most scenarios, although it has been mentioned in this comment that alternatively one could use the `lift` method on the subject and convert the output back to a Subject by casting the result, since `lift` creates an `AnonymousSubject`. However, this may introduce complexities related to understanding the underlying implementation of Subject to ensure the type cast is appropriate.
If you opt for this method, the solution would look like this:
let delayedReplay = <ReplaySubject> new ReplaySubject(1).delay(1000);
// For RxJS 6+ without rxjs-compat:
// let delayedReplay = <ReplaySubject> new ReplaySubject(1).lift(new DelayOperator(1000));
delayedReplay.subscribe((data) => {
console.log('Got:', data);
});
delayedReplay.next('Test');
Please be aware that the `lift` functionality might be removed in RxJS version 7.
An alternative approach is to extend the existing ReplaySubject so that type casting becomes unnecessary. It's important to note that this method will increase the interdependence between your application and RxJS, potentially overlooking the benefits of using composable pipes.
A potential extension can be structured as shown below:
class DelayedReplaySubject<T> extends ReplaySubject<T> {
constructor(buffer: number, private delay: number) {
super(delay);
}
next(value?: T): void {
of(value)
.pipe(delay(this.delay))
.subscribe(val => super.next(val));
}
}
If you're looking to ensure that both future and previous items are emitted with a delay when subscribing
this.eventsQueue$ = new ReplaySubject<AnalyticsEvent>();
this.eventsQueue$.asObservable().pipe(
concatMap(value => of(value).pipe(delay(2000)))
).subscribe((e: AnalyticsEvent) => {
console.log('received event', e.type);
});
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