Hot and general observations with EventEmitter

Question

Is there a way to get the hot observable from EventEmitter(or the equivalent available in Angular 2 alpha 46 / RxJS 5 alpha)? that is , if we sign after the value is resolved, it starts with the previously resolved value . Like what we have when we always return the same promise.

Ideally, only using Angular 2 objects (I read somewhere light RxJS will be later implemented later to remove the dependency), otherwise importing RxJS is fine. AsyncSubject seems to fit my needs, but it is not available in RxJS 5 alpha.

I tried the following, without success (never run). Any idea on how to use it?

let emitter = new EventEmitter<MyObj>();
setTimeout(() => {emitter.next(new MyObj());});
this.observable = emitter;
return this.observable.share();

The full plunker here compares hot and cold

Usecase : for some asynchronous objects, they are available only once (for example, a series of HTTP calls merged / wrapped in a new oneEventEmitter ), but providing a resolved asynchronous object to any service / component that subscribes to it, even if they subscribe after its resolution (answers received HTTP).

EDIT: , HTTP-, (?) EventEmitter , Angular 2 alpha 46/RxJS 5 alpha, / (HTTP - ). myEventEmitter.share() (cf plunker ), Observable, HTTP (cf plunker from @ ). Angular 2 alpha 46,.toRx() , EventEmitter .

promises, . HTTP Angular 2, promises (, , , promises, , promises).

share() ( doc - 5, Angular 2) - Observable, HTTP Angular 2, EventEmitter.

EDIT: , Observable, HTTP, , RxJS .

EDIT: : , HTTP.

!

Answer 1

ReplaySubject , . @robwormald gitter, , .

HTTP:

import {Injectable} from 'angular2/angular2';
import {Http} from 'angular2/http';
import {ReplaySubject} from '@reactivex/rxjs/dist/cjs/Rx'

@Injectable()
export class PeopleService {
  constructor(http:Http) {
    this.people = new ReplaySubject(1);

    http.get('api/people.json')
      .map(res => res.json())
      .subscribe(this.people);
  }
}

:

// ... annotations
export class App {
  constructor(peopleService:PeopleService) {

    people.subscribe(v => {
      console.log(v)
    });

    //some time later

    setTimeout(() => {
      people.subscribe(v => {
        console.log(v)
      });
      people.subscribe(v => {
        console.log(v)
      });
    },2000)
  }
}

EDIT: BehaviorSubject . , , HTTP-.

Answer 2

, , , , , Rx.BehaviourSubject. Rxjs: https://github.com/Reactive-Extensions/RxJS/blob/master/doc/gettingstarted/subjects.md.

:

BehaviourSubject ReplaySubject, , . BehaviourSubject . , . , , .

Rx.AsyncSubject :

AsyncSubject Replay Behavior, . AsyncSubject , , . AsyncSubject - .

:

• : this._coldObservable = emitter.share();. share !
• EventEmitter

: EventEmitter Rx.Observable:

function toRx ( eventEmitter ) {
  return Rx.Observable.create(function ( observer ) {
    eventEmitter.subscribe(function listener ( value ) {observer.onNext(value)});
    // Ideally you also manage error and completion, if that makes sense with Angular2
    return function () {
      /* manage end of subscription here */
    };
  };
)
}

Rx.Observable, share(), shareReplay(1), .

, Angular , , .