javascript - RxJS publishReplay vs publishLast - Stack Overflow

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I am implementing caching HTTP results in Angular application. From what I know both of the following code works, but I need to know if they are doing exactly the same thing, or I am missing something important?

publishLast

getPosts() {
    if( !this.posts$ ) {
      this.posts$ = this.http.get('api').publishLast().refCount();
      return this.posts$;
    }

    return this.posts$;
  }

publishReplay

getPosts() {
  if( !this.posts$ ) {
    this.posts$ = this.http.get('api').publishReplay(1).refCount();
       return this.posts$;
  }

  return this.posts$;
}

I am implementing caching HTTP results in Angular application. From what I know both of the following code works, but I need to know if they are doing exactly the same thing, or I am missing something important?

publishLast

getPosts() {
    if( !this.posts$ ) {
      this.posts$ = this.http.get('api').publishLast().refCount();
      return this.posts$;
    }

    return this.posts$;
  }

publishReplay

getPosts() {
  if( !this.posts$ ) {
    this.posts$ = this.http.get('api').publishReplay(1).refCount();
       return this.posts$;
  }

  return this.posts$;
}

• javascript
• rxjs

Share Improve this question Follow edited Jun 7, 2017 at 12:12 Olaf Horstmann 16.9k66 gold badges6060 silver badges6565 bronze badges asked Jun 7, 2017 at 12:00 undefinedundefined 6,8741313 gold badges5353 silver badges101101 bronze badges

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1 Answer 1

Sorted by: Reset to default 18

publishLast shares (as the name suggests) the last emitted value - which can only be determined when the stream pletes.

publishReplay(1) shares the latest emitted value, which is done after any emission.

---

In the case of this.http.get(...) the behavior is the same, because the stream will plete after the result was received, thus the last and the latest value are the same thing.

You will have a different result though for streams that emit more than one value or that do not plete immediately after the emission of this value.

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