Angular is a popular framework for building dynamic and reactive web applications. It leverages a declarative approach in template code that can be composed with powerful structural directives. Among these directives is the subject, a critical feature in building reactive systems in Angular.

In this article, we will delve into what subjects are, why they are critical in building reactive Angular applications, and how to use them in practice.

## What are subjects?

A subject is a type of observable in Angular that allows you to publish and subscribe to events. The core of the subject is that it has both an observer and an observable interface. The observer property is a function that can receive data, errors, or a completion signal, while the observable property can be subscribed to by other code.

Subjects are excellent for implementing reactive patterns in Angular. A reactive pattern is a programming style where you write programs that are scalable, maintainable, and efficient. Reactive programming is useful in situations where you need to react to a stream of diverse events where traditional programming approaches would not suffice.

Subjects work by emitting values to subscribers, just like traditional observables. But unlike observables, subjects serve as both a source of data as well as an observer. This means we can push data to a subject from one piece of code and subscribe to it from another code unit.

## Why are subjects essential?

Subjects are critical in building reactive Angular applications for several reasons:

1. **Subjects can be subscribed to multiple times:** One of the significant benefits of using subjects is that they can be subscribed to from multiple places. This makes them ideal for sharing data between components in Angular.

2. **Subjects are easy to implement:** Implementing subjects is straightforward, and you can use them with any type of data.

3. **Subjects are flexible:** You can use them for a wide range of applications, for instance, in user interfaces, event processing, and data communication.

4. **Subjects can be used to manage state:** Subjects can be used to manage state in Angular applications. This makes them useful in scenarios where you want to maintain a global state that can be accessed from multiple components.

## How to use subjects in Angular

Now that we know what subjects are and their importance, let us examine how to use them in Angular.

To use subjects in your Angular application, you need to follow these steps:

1. Import the Subject from the rxjs library:

import { Subject } from ‘rxjs’;

2. Create a subject instance:

mySubject: Subject = new Subject();

3. Push data to the subject:


4. Subscribe to the subject to receive data:

this.mySubject.subscribe((data) => {
// Do something with the data

## FAQs

1. **What is the difference between a subject and an observable in Angular?**

A subject is a type of observable that serves as both the publisher and the subscriber. Observables, on the other hand, represent a stream of data that can be subscribed to by observers.

2. **When should I use subjects in Angular?**

Use subjects when you need to broadcast data to multiple parts of your application or when you want a communication channel between parts of your application.

3. **What are some best practices when using subjects in Angular?**

Always ensure to unsubscribe from a subject subscription when it is no longer needed to prevent memory leaks. Additionally, avoid overusing subjects, as they can lead to overcomplicated systems and obscure code.

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