I am coming back a few months later to my original question and wanted to share the gained knowledge in the meanwhile. I will use the following code as an explanation support (jsfiddle): var ta_count = document.getElementById(‘ta_count’); var ta_result = document.getElementById(‘ta_result’); var threshold = 3; function emits ( who, who_ ) {return function ( x … Read more
Avoiding nested subscriptions depends on the nature of the observables and how they depend on each other: Co-dependent observables When an observable (this.grants.get()) depends on the notification from another observable (this.user), you could use any of the RxJS higher order mapping operators switchMap, mergeMap, concatMap and exhaustMap. Each has their own purpose. You could find … Read more
I think that you need to import this: import ‘rxjs/add/operator/map’ Or more generally this if you want to have more methods for observables. WARNING: This will import all 50+ operators and add them to your application, thus affecting your bundle size and load times. import ‘rxjs/Rx’; See this issue for more details.
What are you people talking about!!! OK so there’s two reasons to unsubscribe from any observable. Nobody seems to be talking much about the very important second reason! Clean up resources. As others have said this is a negligible problem for HTTP observables. It’ll just clean itself up. Prevent the subscribe handler from being run. … Read more
A BehaviorSubject holds one value. When it is subscribed it emits the value immediately. A Subject doesn’t hold a value. Subject example (with RxJS 5 API): const subject = new Rx.Subject(); subject.next(1); subject.subscribe(x => console.log(x)); Console output will be empty BehaviorSubject example: const subject = new Rx.BehaviorSubject(0); subject.next(1); subject.subscribe(x => console.log(x)); Console output: 1 In … Read more
BehaviorSubject is a type of subject, a subject is a special type of observable so you can subscribe to messages like any other observable. The unique features of BehaviorSubject are: It needs an initial value as it must always return a value on subscription even if it hasn’t received a next() Upon subscription, it returns … Read more
What is the difference between Promises and Observables?
EDIT: as of 2021, the proper way is to use the shareReplay operator natively proposed by RxJs. See more details in below answers. Cache the data and if available cached, return this otherwise make the HTTP request. import {Injectable} from ‘@angular/core’; import {Http, Headers} from ‘@angular/http’; import {Observable} from ‘rxjs/Observable’; import ‘rxjs/add/observable/of’; //proper way to … Read more
TL;DR For this question there are two kinds of Observables – finite value and infinite value. http Observables produce finite (1) values and something like a DOM event listener Observable produces infinite values. If you manually call subscribe (not using async pipe), then unsubscribe from infinite Observables. Don’t worry about finite ones, RxJs will take … Read more