defaultIfEmpty

signature: defaultIfEmpty(defaultValue: any): Observable

Emit given value if nothing is emitted before completion.

Examples

Example 1: Default for empty value

( jsBin |
jsFiddle )

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

Example 2: Default for Observable.empty

( jsBin |
jsFiddle )

import { defaultIfEmpty } from 'rxjs/operators';
import { empty } from 'rxjs/observable/empty';
//empty observable
const empty = empty();
//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