concatAll

signature: concatAll(): Observable

Collect observables and subscribe to next when previous completes.


:warning: Be wary of backpressure when the source emits at a faster pace than inner observables complete!

:bulb: In many cases you can use concatMap as a single operator instead!


Examples

( example tests )

Example 1: concatAll with observable

( jsBin | jsFiddle )

//emit a value every 2 seconds
const source = Rx.Observable.interval(2000);
const example = source
  //for demonstration, add 10 to and return as observable
  .map(val => Rx.Observable.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

( jsBin | jsFiddle )

//create and resolve basic promise
const samplePromise = val => new Promise(resolve => resolve(val));
//emit a value every 2 seconds
const source = Rx.Observable.interval(2000);

const example = source
  .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

( jsBin | jsFiddle )

const obs1 = Rx.Observable.interval(1000).take(5);
const obs2 = Rx.Observable.interval(500).take(2);
const obs3 = Rx.Observable.interval(2000).take(1);
//emit three observables
const source = Rx.Observable.of(obs1, obs2, obs3);
//subscribe to each inner observable in order when previous completes
const example = source.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));

Additional Resources


:file_folder: Source Code: https://github.com/ReactiveX/rxjs/blob/master/src/operator/concatAll.ts

results matching ""

    No results matching ""