How to use the defaultIfEmpty function from rxjs

Find comprehensive JavaScript rxjs.defaultIfEmpty code examples handpicked from public code repositorys.

rxjs.defaultIfEmpty is an operator in the RxJS library that emits a default value if the source observable completes without emitting any values.

index.js

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return from(RoasFacebook({ user_id }).ad.get_from_db({ ad_id })).pipe(
    concatMap(identity),
    rxfilter((ad) => !isEmpty(ad)),
    rxmap(Facebook.ad.details),
    defaultIfEmpty({}),
    catchError((error) => {
        console.log("Facebook:ad:db:get:error");
        console.log(error);
        return rxof({ ad_id, error: true });

+ 19 other calls in file

How does rxjs.defaultIfEmpty work?

defaultIfEmpty is a RxJS operator that returns an observable with a default value if the source observable is empty, otherwise it emits the values of the source observable.

When an observable completes without emitting any values, it is considered as an empty observable. In such a case, defaultIfEmpty operator subscribes to the source observable and waits for its completion. If the source observable is empty, defaultIfEmpty operator emits the default value provided by the user. If the source observable emits any value, defaultIfEmpty operator simply passes them through.

The defaultIfEmpty operator can be useful in scenarios where we need to ensure that the observer always receives a value even if the source observable is empty.

Ai Example

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import { of } from "rxjs";
import { defaultIfEmpty } from "rxjs/operators";

const source = of();
const example = source.pipe(defaultIfEmpty("Observable is empty"));
example.subscribe(console.log); // Output: 'Observable is empty'

In this example, the of function from RxJS is used to create an observable that emits no values. The defaultIfEmpty operator is then used to emit a default value of 'Observable is empty' if the source observable emits no values. Finally, the subscribe method is called on the resulting observable to log the emitted value. Since the source observable is empty, the output is the default value of 'Observable is empty'.

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