I'm attempting to deconstruct this specific code snippet to comprehend it better. The new BehaviourSubject appears to be a function call, but I'm confused about what it's doing there. Is it instructing the function BehaviourSubject to have a return type of User? Please clarify this for me in a way that's easy to understand.
this.userSubject = new BehaviorSubject<User>(JSON.parse(localStorage.getItem('user')));
BehaviorSubject is a powerful tool that requires an initial value and emits the current value to new subscribers. The initial value is fetched from localStorage, making it easy to work with stored data.
To access the initial value later, simply add subscribers to this.userSubject.
When using new BehaviorSubject<User>, the angle brackets <> signify that BehaviorSubject is a generic class and User serves as a generic type parameter.
For illustration, consider the following example:
// RxJS v6+
import { BehaviorSubject } from 'rxjs';
const subject = new BehaviorSubject(123);
// Two new subscribers will receive the initial value => output: 123, 123
subject.subscribe(console.log);
subject.subscribe(console.log);
// Both subscribers will now get the new value => output: 456, 456
subject.next(456);
// A new subscriber will receive the latest value (456) => output: 456
subject.subscribe(console.log);
// All three subscribers will be updated with the new value => output: 789, 789, 789
subject.next(789);
// Final output sequence: 123, 123, 456, 456, 456, 789, 789, 789
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