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RXJS OPERATORS:

Operators are a very essential part of RXJS. It allows complex asynchronous code to be composed in a declarative manner.

  1. interval operator: It’s a function that takes in number as an argument and outputs an observable.
import {interval} from 'rxjs';

2. take operator: It’s a filter that emits first counts values emitted by observable.

import { interval } from 'rxjs';

SUBJECTS in RXJS

A subject is a special observable whose value can be multicasted into many observers. While plain Observable is unicast i.e each subscribed observer has its own execution state.

Code to show Observable is unicast

import {Observable} from 'rxjs';

Code to show Subject is Multicast

import {Subject} from 'rxjs';

BehaviorSubject

  1. It stores the latest value emitted to observers.
  2. When a new observer subscribes, it will immediately receive current value.
  3. It is useful for representing values over time.

Code Without BehaviorSubject(Normal subject)

import {Subject} from 'rxjs';

NOTE: If you noticed carefully when a new observer subscribed to the subject, the latest value was 0, but that was not emitted to the new observer. This is the drawback of a normal subject(Subject). Hence, we use BehaviorSubject.

Code With BehaviorSubject

import {BehaviorSubject} from 'rxjs';

NOTE: If you noticed carefully when a new observer subscribed to the subject, the latest value was 0, and now that was emitted to the new observer.

ReplaySubject

It is similar to BehaviorSubject and records or remembers multiple old values and emits them to new subscribers.

import {ReplaySubject} from 'rxjs';

NOTE: If you noticed carefully, the ReplaySubject in created with buffer 3 values for a new subscriber. Hence, when the second new subscriber subscribed to the subject, they got the last three values emitted by the replayObservable.

AsyncSubject

  1. It only emits the last value of the Observable execution and only when the execution completes.

AsyncSubject code without complete

import {AsyncSubject} from 'rxjs';

NOTE: If you notice carefully, asyncSubject not yet completed. Hence, no value is emitted by asynSubject.

Now see the below code pretty similar to the above code but just once change.

import {AsyncSubject} from 'rxjs';