Observable from a string (Angular 2)

Question

I am pretty new to Observables. How would I create Observable just from a simple string? Then subscribe to it and output it when it changes.

Does that make sense?

I don't have any luck with google search. Probably wrong keywords?

Adding some code for better explanation:

My constructor on service

constructor() {
  // Create observable stream to output our data
  this.notice = Observable.create(
    (observer) => this.observer = observer;
  );
};

My method on service

set(string) {
  this.notice.subscribe((value) => {
    // Push the new value into the observable stream
    this.observer.next(string);
  }, (error) => console.log('Could not set data.'));
}

Calling service method 

setNotice(event) {
  event.preventDefault();

  // Calling service to set notice
  this.noticeService.set('This is a string');
}

I think I am doing something wrong here? But not sure how to ask. I would be grateful for any of the explanations.

Waht about this.notice.unsubscribe() in ngDestroy() too? I know that's a common cause of memory leaks for manually added event listeners... So I presume this would be the same. — JGFMK, Aug 11 '17 at 18:55
I'd also be considering BehaviorSubject too for this. https://stackoverflow.com/questions/39494058/behaviorsubject-vs-observable — JGFMK, Aug 11 '17 at 18:57

score 19 · Accepted Answer · edited May 11 '19 at 19:49

19

You can use the of method of the Observable class:

var obs = Observable.of('some string');

Edit

Regarding the code of your service, I would refactor the code of your set method like this:

set(string) {
  this.observer.next(string);
}

You can subscribe on the notice property in another part of your application to be notified.

edited May 11 '19 at 19:49

Saksham

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answered Feb 22 '16 at 14:55

Thierry Templier

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thank you for showing this. I am wondering how to make 'some string' as a value of variable that could change. How to push it inside Observable then? – be-codified Feb 22 '16 at 15:07
In fact, you can't. That said you can fire event when the value changes. For this you need to create a raw observable: `Observable.create((observer) => { observer.next('some string'); });`. The `next` method can be called several times... Note that you can set the `observer` variable into a variable outside the callback. – Thierry Templier Feb 22 '16 at 15:12
1

You're welcome! I think the problem is at the level of your `set` method. I updated my answer... – Thierry Templier Feb 22 '16 at 16:09
1

I would create the observable without the word observable `var obs = of('some string');` – Mike Poole Apr 01 '20 at 08:59

score 1 · Answer 2 · edited Feb 25 '23 at 18:36

I found out that we can create an Observable by using method "of" from the rxjs library. Because I had difficulties using the method "Observable.of" from the previous answer, I'm giving you my solution.

import {
  Observable,
  of,
} from 'rxjs';

  //message2: string = '...';  // old code
  message2$: Observable<any>;
  
  ngOnInit():void {
    this.message2$ = of('...');
  }

Full example on StackBlitz.

Observable from a string (Angular 2)

2 Answers2