BehaviorSubject vs Observable : RxJS has observers and observables, Rxjs offers a multiple classes to use with data streams, and one of them is a BehaviorSubject.
Observables : Observables are lazy collections of multiple values over time.
BehaviorSubject:A Subject that requires an initial value and emits its current value to new subscribers.
// RxJS v6+
import { BehaviorSubject } from 'rxjs';
const subject = new BehaviorSubject(123);
//two new subscribers will get initial value => output: 123, 123
subject.subscribe(console.log);
subject.subscribe(console.log);
//two subscribers will get new value => output: 456, 456
subject.next(456);
//new subscriber will get latest value (456) => output: 456
subject.subscribe(console.log);
//all three subscribers will get new value => output: 789, 789, 789
subject.next(789);
// output: 123, 123, 456, 456, 456, 789, 789, 789