rxjs

RXJS Wait for all observables in an array to complete (or error)

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If you want to compose an observable that emits when all of the source observables complete, you can use forkJoin: import { Observable } from ‘rxjs/Observable’; import ‘rxjs/add/observable/forkJoin’; import ‘rxjs/add/operator/first’; var tasks$ = []; tasks$.push(Observable.timer(1000).first()); tasks$.push(Observable.timer(3000).first()); tasks$.push(Observable.timer(10000).first()); Observable.forkJoin(…tasks$).subscribe(results => { console.log(results); });

Node.js Streams vs. Observables

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Both Observables and node.js’s Streams allow you to solve the same underlying problem: asynchronously process a sequence of values. The main difference between the two, I believe, is related to the context that motivated its appearance. That context is reflected in the terminology and API. On the Observables side you have an extension to EcmaScript … Read more

Angular async pipe and object property [duplicate]

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The error is surprisingly accurate as the *ngIf directive expects true or false and uses the resulting expression to determine whether or not to render the HTML element in the DOM. EXCEPTION: Invalid argument ‘true’ for pipe ‘AsyncPipe’ in [!user$.anonymouse | async in SettingsPage@27:22] The expression you have is user$.anonymouse which evaluates as truthy, but … Read more

How to return observable from subscribe

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You can’t return an observable from subscribe but if you use map instead of subscribe then an Observable is returned. canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot):Observable<boolean> { // get route to be activated this.routeToActivate = route.routeConfig.path; // get user access levels return this._firebase.isUserAdminObservable .map(user => { // do something here // user.access_level; return true; }) .first(); // … Read more

Best way to import Observable from rxjs

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Rxjs v 6.* It got simplified with newer version of rxjs . 1) Operators import {map} from ‘rxjs/operators’; 2) Others import {Observable,of, from } from ‘rxjs’; Instead of chaining we need to pipe . For example Old syntax : source.map().switchMap().subscribe() New Syntax: source.pipe(map(), switchMap()).subscribe() Note: Some operators have a name change due to name collisions … Read more

Child listens for parent event in Angular 2

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For the sake of posterity, just thought I’d mention the more conventional solution to this: Simply obtain a reference to the ViewChild then call one of its methods directly. @Component({ selector: ‘app-child’ }) export class ChildComponent { notifyMe() { console.log(‘Event Fired’); } } @Component({ selector: ‘app-parent’, template: `<app-child #child></app-child>` }) export class ParentComponent { @ViewChild(‘child’) … Read more

RxJS sequence equivalent to promise.then()?

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For data flow (equivalent to then): Rx.Observable.fromPromise(…) .flatMap(function(result) { // do something }) .flatMap(function(result) { // do something }) .subscribe(function onNext(result) { // end of chain }, function onError(error) { // process the error }); A promise can be converted into an observable with Rx.Observable.fromPromise. Some promise operators have a direct translation. For instance RSVP.all, … Read more

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