Behavior subject is the most common subject in angular. The Behavior subject represents the current value and it is imported from the Rxjs library. It is similar to the subject but the difference is that we can set the initial value in the behavior subject.

Let’s say we want to store username but we want to change it. We want to store an initial name and also be able to access the current value. You can get the last emitted value from the behavior subject.

Behavior subject will always return a value, even if no data has been emitted from the subscriber.

You can import behavior subject from the ‘rxjs’ or ‘rxjs/BehaviorSubject library’.

Load the data once or when we need the data.

When the data changes then notify the value that is subscribing to the Behavior Subject.

Keep the data updated automatically across the application.

Remove unnecessary requests to load the data just for the cause of ensuring that the data is already loaded.

Let’s see an example of Behavior Subject:

There are few things happening here:

Let’s see another example of Behavior Subject:

Instantiate new behavior subject with the initial value: In this example, the initial value is number (10).

To get the current value, you can use the getValue() method:

You should see an output: Current Value: 10

You can change the value of an existing behavior subject using the next () method with the new value.

After that you can call the getValue() method, then you can acquire the current value.

You should see an output: Current Value: 30