concatAll

function stable

Converts a higher-order Observable into a first-order Observable by concatenating the inner Observables in order.

`concatAll<O extends ObservableInput<any>>(): OperatorFunction<O, ObservedValueOf<O>>`

Parameters

There are no parameters.

Returns

OperatorFunction<O, ObservedValueOf<O>>: A function that returns an Observable emitting values from all the inner Observables concatenated.

Description

Flattens an Observable-of-Observables by putting one inner Observable after the other.

concatAll marble diagram

Joins every Observable emitted by the source (a higher-order Observable), in a serial fashion. It subscribes to each inner Observable only after the previous inner Observable has completed, and merges all of their values into the returned observable.

Warning: If the source Observable emits Observables quickly and endlessly, and the inner Observables it emits generally complete slower than the source emits, you can run into memory issues as the incoming Observables collect in an unbounded buffer.

Note: concatAll is equivalent to mergeAll with concurrency parameter set to 1.

Example

For each click event, tick every second from 0 to 3, with no concurrency

import { fromEvent, interval } from 'rxjs';
import { map, take, concatAll } from 'rxjs/operators';

const clicks = fromEvent(document, 'click');
const higherOrder = clicks.pipe(
  map(ev => interval(1000).pipe(take(4))),
);
const firstOrder = higherOrder.pipe(concatAll());
firstOrder.subscribe(x => console.log(x));

// Results in the following:
// (results are not concurrent)
// For every click on the "document" it will emit values 0 to 3 spaced
// on a 1000ms interval
// one click = 1000ms-> 0 -1000ms-> 1 -1000ms-> 2 -1000ms-> 3