The difference between Subject and BehaviorSubject in Rxjs

Through a practical example to understand.

The following code creates a new subject and then calls the next method to multicast it to all its listeners.

import { Subject } from 'rxjs';

const jerry = new Subject();

const subscription = jerry.subscribe((data) => console.log(data));

console.log('ok');
jerry.next(111);
jerry.next(222);

subscription.unsubscribe();
console.log('?');
jerry.next(333);

The above example will print 111, 222

If the Subject starts multicasting before being subscribed (that is, 111 in line 5 of the figure below), then these multicast values will not be received by the subscribers after starting the multicast. As shown in the figure below: the subscriber will only print the multicast value 222 received after subscribing to the subject:

Using BehaviorSubject, you can avoid this problem: even before the subscriber subscribes to the subject, the latter starts to call next for multicast, these multicast values can also be received by the subscriber: