BehaviorSubject firing twice

Question

Im using BehaviourSubject from RxJS:

private rights = new BehaviorSubject<Array<string>>([]);


updateRights(rights: Array<string>) {
  this.rights.next(rights);
}

getRights(): Observable<any> {
  return this.rights.asObservable();
}

I'm updating the rights in the root component and im subscribing to it in another component like:

 this.configService.getRights().subscribe(res => {
   console.log(res);
 })

This subscription is firing twice. Once when the data is empty and then again when the data is received.

I want the subscription to fire only once and get only the latest data. What should be done?

djolf · Answer 1 · 2019-05-16T02:41:06.067

8

BehaviourSubject emits the value on subscription by default, and it is intended design. If you do not want this behaviour, use Subject instead.

edited May 16 '19 at 02:41

answered May 15 '19 at 09:04

djolf

1,196
6
18

1

This is the correct answer. When using rxjs, its very important to know the difference between Subject, BehaviorSubject and ReplaySubject (ReplaySubject isnt used that much, usually you will use Subject or BehaviorSubject). – Davy May 15 '19 at 13:11

Masoud Bimmar · Answer 2 · 2019-05-15T09:24:01.690

0

Do it this way:

private currnetRightsSubject: BehaviorSubject<string[]>;
public currentRights: Observable<string[]>;

constructor() {
    this.currnetRightsSubject= new BehaviorSubject<string[]>(/*.......*/);
    this.currentRights= this.currnetRightsSubject.asObservable();
}

public get currentRightsValue(){
    return this.currnetRightsSubject.value;
}

updated

fill the BehaviorSubject like this:

this.currnetRightsSubject.next(someValue);

edited May 15 '19 at 09:24

answered May 15 '19 at 08:58

Masoud Bimmar

6,941
4
30
33

Property 'value' does not exist on type 'Observable' – Mohit Harshan May 15 '19 at 09:06
tried it. Now it doesnt wait for value.its showing empty array – Mohit Harshan May 15 '19 at 09:18
you must put value in behaviorSubject first, i update the answer – Masoud Bimmar May 15 '19 at 09:23
check my question ..i am doing this in the updateRights function – Mohit Harshan May 15 '19 at 09:24
i removed .value from get current rights value function ..and the behaviour subject returns.the problem is getting the valuefrom it .value doesnt work – Mohit Harshan May 15 '19 at 09:26
its wrong, you put rights inside rights again, just provide some string for BS – Masoud Bimmar May 15 '19 at 09:30
i want to push array to the behaviour subject not string – Mohit Harshan May 15 '19 at 09:35
Array of strings – Mohit Harshan May 15 '19 at 09:35
the thing is only triggereing once but its before the value is received.. im updating rights in the root component,but the behaviour subject doesnt wait for the updation – Mohit Harshan May 15 '19 at 09:43
see this [BehaviorSubject vs Observable?](https://stackoverflow.com/a/40231605/2126355) – Masoud Bimmar May 15 '19 at 09:45
ya.ok ..the problem with using subects is that im not able to wait for the response – Mohit Harshan May 15 '19 at 10:45
i resolved it using take operator from rxjs using the same behaviour subject as in my question – Mohit Harshan May 15 '19 at 11:42

BehaviorSubject firing twice

2 Answers2