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angulartypescriptrxjsbehaviorsubjectsubject

What is the difference between Subject and BehaviorSubject?

I'm not clear on the difference between a Subject and a BehaviorSubject. Is it just that a BehaviorSubject has the getValue() function?

Solution

  • A BehaviorSubject holds one value. When it is subscribed it emits the value immediately. A Subject doesn't hold a value.

    Subject example (with RxJS 5 API):

    const subject = new Rx.Subject();
subject.next(1);
subject.subscribe(x => console.log(x));

    Console output will be empty

    BehaviorSubject example:

    const subject = new Rx.BehaviorSubject(0);
subject.next(1);
subject.subscribe(x => console.log(x));

    Console output: 1

    In addition:

    • BehaviorSubject should be created with an initial value: new Rx.BehaviorSubject(1)
    • Consider ReplaySubject if you want the subject to get previously published values.