Collect observables and subscribe to next when previous completes.
:warning: Be wary of when the source emits at a faster pace than inner observables complete!
:bulb: In many cases you can use as a single operator instead!
Examples
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Example 1: concatAll with observable
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// RxJS v6+
import { map, concatAll } from 'rxjs/operators';
import { of, interval } from 'rxjs';
//emit a value every 2 seconds
const source = interval(2000);
const example = source.pipe(
//for demonstration, add 10 to and return as observable
map(val => of(val + 10)),
//merge values from inner observable
concatAll()
);
//output: 'Example with Basic Observable 10', 'Example with Basic Observable 11'...
const subscribe = example.subscribe(val =>
console.log('Example with Basic Observable:', val)
);
Example 2: concatAll with promise
// RxJS v6+
import { map, concatAll } from 'rxjs/operators';
import { interval } from 'rxjs';
//create and resolve basic promise
const samplePromise = val => new Promise(resolve => resolve(val));
//emit a value every 2 seconds
const source = interval(2000);
const example = source.pipe(
map(val => samplePromise(val)),
//merge values from resolved promise
concatAll()
);
//output: 'Example with Promise 0', 'Example with Promise 1'...
const subscribe = example.subscribe(val =>
console.log('Example with Promise:', val)
);
Example 3: Delay while inner observables complete
// RxJS v6+
import { take, concatAll } from 'rxjs/operators';
import { interval, of } from 'rxjs/observable/interval';
const obs1 = interval(1000).pipe(take(5));
const obs2 = interval(500).pipe(take(2));
const obs3 = interval(2000).pipe(take(1));
//emit three observables
const source = of(obs1, obs2, obs3);
//subscribe to each inner observable in order when previous completes
const example = source.pipe(concatAll());
/*
output: 0,1,2,3,4,0,1,0
How it works...
Subscribes to each inner observable and emit values, when complete subscribe to next
obs1: 0,1,2,3,4 (complete)
obs2: 0,1 (complete)
obs3: 0 (complete)
*/
const subscribe = example.subscribe(val => console.log(val));
