Angular

What is the difference between BehaviorSubject and Observable in Angular?

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What is the difference between BehaviorSubject and Observable?

Angular is an extremely powerful framework, offering various features and tools. Of all of them, one of the most critical and important features is to deal with asynchronous operations by implementing BehaviorSubject and Observable; the former and the latter are essentially the key modules of the RxJS library. It further helps us in managing the flow of data reactively. This article will handle the basics of BehaviorSubject and Observable in Angular, along with the basic implementation & differences of both.

BehaviorSubject

This is the subject, that is, an extension of the observable in the RxJS library, which not only provides a stream of data but also preserves the most recent value or latest value to the subscribers. It's both observer and observable at the same time. It means that if a late subscriber arrives, they immediately get the latest value present. This is an advantage for BehaviorSubject when the current state is important and subscribers should be able to access values immediately next to the most recently emitted value.

Example:

Creating a BehaviorSubject

You create a BehaviorSubject by importing the BehaviorSubject class from the RxJS library and initializing it with some initial value:

import { BehaviorSubject } from 'rxjs';const myBehaviorSubject = new BehaviorSubject(initialValue);

Subscription to a BehaviorSubject

Subscription to BehaviorSubject is very much like a subscription to simple Observable:

myBehaviorSubject.subscribe(value => console.log(`Received value: ${value}`),error => console.error(`Error: ${error}`), () => console.log('BehaviorSubject completed') );

Updating the BehaviorSubject

you can update the value of a BehaviorSubject using the next method, which will emit a new value to all its subscribed observers:

myBehaviorSubject.next(newValue);

Observables

Observable The flow of data, which can be observed over a period of time, represents an observable. It helps in asynchronous operations well, which means components react to the changes by subscribing to it. Those subscribers receive values only after their subscription; this is unlike the BehaviorSubject which gets the latest value. These are much like immutable, which cannot access any previous values before subscription.

Example:

import { Observable } from 'rxjs';// Create an Observable that emits a sequence of valuesconst myObservable = new Observable(observer => { observer.next(‘My First observable); observer.next(‘My Second observable’); observer.next(‘My Third observable’); observer.complete();});// Subscribe to the ObservablemyObservable.subscribe( value => console.log(`Next value: ${value}`), error => console.error(`Error: ${error}`), () => console.log('Complete!'));// Output: Next value: My First observable// Output: Next value: My Second observable// Output: Next value: My Third observable// Output: Complete!

Difference between BehaviorSubject and Observable

Observable

Initialization

BehaviorSubject: Provides an initial value that is emitted immediately upon subscription. Observable: No initial value

Immediate Emit

BehaviorSubject:Sends the most recent value and all future updates to new subscribers. Observable: Produces values over time that occur after the subscription.

Last value memory

BehaviorSubject: Stores the most recent value. Observable: Do not store previous ones.

Flexibility

BehaviorSubject: More intricate, applied when components require instant access to the current state or values. Observable: Straightforward, used when a one-way data flow is required.

Use Case

BehaviorSubject: Beneficial when we want subscribers to receive the latest value. Observable: Ideal when previous values are not significant.

Example

BehaviorSubject: Preserving the current user state within an application. Observable: Regular data updates.

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