Angular2 @ TypeScript Observable error
<p>I have an input field and when the user types a search string I want to wait for the user to stop typing for at least 300 milliseconds (debounce) before doing a _heroService http request. Only changed search values make it through to the service (distinctUntilChanged). The switchMap returns a new observable that combines these _heroService observables, re-arranges them in their original request order, and delivers to subscribers only the most recent search results.</p>

<p>I am using Angular 2.0.0-beta.0 and TypeScript 1.7.5. </p>

<p>How do I get this thing working correct?</p>

<p>I get compile error:</p>

<pre><code>Error:(33, 20) TS2345: Argument of type '(value: string) =&gt; Subscription&lt;Hero[]&gt;' is not assignable to parameter of type '(x: {}, ix: number) =&gt; Observable&lt;any&gt;'.Type 'Subscription&lt;Hero[]&gt;' is not assignable to type 'Observable&lt;any&gt;'. Property 'source' is missing in type 'Subscription&lt;Hero[]&gt;'.
Error:(36, 31) TS2322: Type 'Hero[]' is not assignable to type 'Observable&lt;Hero[]&gt;'. Property 'source' is missing in type 'Hero[]'.
</code></pre>

<p>Run time error (after typing first key in search input field):</p>

<pre><code>EXCEPTION: TypeError: unknown type returned
STACKTRACE:
TypeError: unknown type returned
at Object.subscribeToResult (http://localhost:3000/rxjs/bundles/Rx.js:7082:25)
at SwitchMapSubscriber._next (http://localhost:3000/rxjs/bundles/Rx.js:5523:63)
at SwitchMapSubscriber.Subscriber.next (http://localhost:3000/rxjs/bundles/Rx.js:9500:14)
...
-----async gap----- Error at _getStacktraceWithUncaughtError 
EXCEPTION: Invalid argument '[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]' for pipe 'AsyncPipe' in [heroes | async in Test@4:16]
</code></pre>

<p>test1.ts</p>

<pre><code>import {bootstrap}         from 'angular2/platform/browser';
import {Component}         from 'angular2/core';
import {HTTP_PROVIDERS}    from 'angular2/http';

import {Observable}        from 'rxjs/Observable';
import {Subject}           from 'rxjs/Subject';
import 'rxjs/Rx';

import {Hero}              from './hero';
import {HeroService}       from './hero.service';

@Component({
    selector: 'my-app',
    template: `
        &lt;h3&gt;Test&lt;/h3&gt;
        Search &lt;input #inputUser (keyup)="search(inputUser.value)"/&gt;&lt;br&gt;
        &lt;ul&gt;
            &lt;li *ngFor="#hero of heroes | async"&gt;{{hero.name}}&lt;/li&gt;
        &lt;/ul&gt;
    `,
    providers: [HeroService, HTTP_PROVIDERS]
})

export class Test {

    public errorMessage: string;

    private _searchTermStream = new Subject&lt;string&gt;();

    private heroes: Observable&lt;Hero[]&gt; = this._searchTermStream
        .debounceTime(300)
        .distinctUntilChanged()
        .switchMap((value: string) =&gt;
            this._heroService.searchHeroes(value)
                .subscribe(
                    heroes =&gt; this.heroes = heroes,
                    error =&gt;  this.errorMessage = &lt;any&gt;error)
        )

    constructor (private _heroService: HeroService) {}

    search(value: string) {
        this._searchTermStream.next(value);
    }
}

bootstrap(Test);
</code></pre>

<p>hero.ts</p>

<pre><code>export interface Hero {
    _id: number,
    name: string
}
</code></pre>

<p>hero.service.ts</p>

<pre><code>import {Injectable}     from 'angular2/core';
import {Http, Response} from 'angular2/http';
import {Headers, RequestOptions} from 'angular2/http';
import {Observable}     from 'rxjs/Observable';
import 'rxjs/Rx';

import {Hero}           from './hero';

@Injectable()

export class HeroService {

    private _heroesUrl = 'api/heroes';

    constructor (private http: Http) {}

    getHeroes () {
        return this.http.get(this._heroesUrl)
            .map(res =&gt; &lt;Hero[]&gt; res.json())
            .do(data =&gt; console.log(data))
            .catch(this.handleError);
    }

    searchHeroes (value) {
        return this.http.get(this._heroesUrl + '/search/' + value )
            .map(res =&gt; &lt;Hero[]&gt; res.json())
            .do(data =&gt; console.log(data))
            .catch(this.handleError);
    }

    addHero (name: string) : Observable&lt;Hero&gt;  {

        let body = JSON.stringify({name});
        let headers = new Headers({ 'Content-Type': 'application/json' });
        let options = new RequestOptions({ headers: headers });

        return this.http.post(this._heroesUrl, body, options)
            .map(res =&gt;  &lt;Hero&gt; res.json())
            .do(data =&gt; console.log(data))
            .catch(this.handleError)
    }

    private handleError (error: Response) {
        // in a real world app, we may send the server to some remote logging infrastructure
        // instead of just logging it to the console
        console.log(error);
        return Observable.throw('Internal server error');
    }
}
</code></pre>

<p>index.html</p>

<pre><code>&lt;!DOCTYPE html&gt;
&lt;html&gt;
  &lt;head&gt;
    &lt;base href="/"&gt;
    &lt;script src="angular2/bundles/angular2-polyfills.js"&gt;&lt;/script&gt;
    &lt;script src="typescript/lib/typescript.js"&gt;&lt;/script&gt;
    &lt;script src="systemjs/dist/system.js"&gt;&lt;/script&gt;
    &lt;script src="angular2/bundles/router.dev.js"&gt;&lt;/script&gt;
    &lt;script src="rxjs/bundles/Rx.js"&gt;&lt;/script&gt;
    &lt;script src="angular2/bundles/angular2.js"&gt;&lt;/script&gt;
    &lt;script src="angular2/bundles/http.dev.js"&gt;&lt;/script&gt;
    &lt;link rel="stylesheet" href="node_modules/bootstrap/dist/css/bootstrap.min.css"&gt;
    &lt;script&gt;
      System.config({
        transpiler: 'typescript',
        typescriptOptions: { emitDecoratorMetadata: true },
        packages: {'components': {defaultExtension: 'ts'}}
      });
      System.import('components/test1')
            .then(null, console.error.bind(console));
    &lt;/script&gt;
  &lt;/head&gt;
  &lt;body&gt;
    &lt;my-app&gt;Loading...&lt;/my-app&gt;
  &lt;/body&gt;
&lt;/html&gt;
</code></pre>

<p>Here is another version 'test2.ts' that works fine doing a http request after every (keyup) event:</p>

<pre><code>import {bootstrap}         from 'angular2/platform/browser';
import {Component}         from 'angular2/core';
import {HTTP_PROVIDERS}    from 'angular2/http';

import {Hero}              from './hero';
import {HeroService}       from './hero.service';

@Component({
    selector: 'my-app',
    template: `
        &lt;h3&gt;Test&lt;/h3&gt;
        Search &lt;input #inputUser (keyup)="search(inputUser.value)"/&gt;&lt;br&gt;
        &lt;ul&gt;
            &lt;li *ngFor="#hero of heroes"&gt;{{hero.name}}&lt;/li&gt;
        &lt;/ul&gt;
    `,
    providers: [HeroService, HTTP_PROVIDERS]
})

export class Test {

    public heroes:Hero[] = [];
    public errorMessage: string;

    constructor (private _heroService: HeroService) {}

    search(value: string) {
        if (value) {
            this._heroService.searchHeroes(value)
                .subscribe(
                    heroes =&gt; this.heroes = heroes,
                    error =&gt;  this.errorMessage = &lt;any&gt;error);
        }
        else {
            this.heroes = [];
        }
    }
}

bootstrap(Test);
</code></pre>