ConcatWith

Emits all of the values from the source observable, then, once it completes, subscribes to each observable source provided, one at a time, emitting all of their values, and not subscribing to the next one until it completes.

Syntax

concatWith<T, A extends readonly unknown[]>(...otherSources: any[]): OperatorFunction<T, T | A[number]>

Parameters	Description
otherSources	Other observable sources to subscribe to, in sequence, after the original source is complete.

Returns

A function that returns an Observable that concatenates subscriptions to the source and provided Observables subscribing to the next only once the current subscription completes.

Example

Listen for one mouse click, then listen for all mouse moves.

import { fromEvent } from 'rxjs';
import { concatWith } from 'rxjs/operators';
 
const clicks$ = fromEvent(document, 'click');
const moves$ = fromEvent(document, 'mousemove');
 
clicks$.pipe(
  map(() => 'click'),
  take(1),
  concatWith(
    moves$.pipe(
      map(() => 'move')
    )
  )
)
.subscribe(x => console.log(x));
 
// 'click'
// 'move'
// 'move'
// 'move'
// ...