defaultIfEmpty

signature: defaultIfEmpty(defaultValue: any): Observable

Emit given value if nothing is emitted before completion.

Examples

Example 1: Default for empty value

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// RxJS v6+
import { defaultIfEmpty } from 'rxjs/operators';
import { of } from 'rxjs';

//emit 'Observable.of() Empty!' when empty, else any values from source
const exampleOne = of().pipe(defaultIfEmpty('Observable.of() Empty!'));
//output: 'Observable.of() Empty!'
const subscribe = exampleOne.subscribe(val => console.log(val));

Example 2: Default for Observable.empty

( Stackblitz | jsBin | jsFiddle )

// RxJS v6+
import { defaultIfEmpty } from 'rxjs/operators';
import { empty } from 'rxjs';

//emit 'Observable.empty()!' when empty, else any values from source
const example = empty().pipe(defaultIfEmpty('Observable.empty()!'));
//output: 'Observable.empty()!'
const subscribe = example.subscribe(val => console.log(val));

Additional Resources

• defaultIfEmpty - Official docs

Source Code: https://github.com/ReactiveX/rxjs/blob/master/src/internal/operators/defaultIfEmpty.ts