concatMapTo - 2

RxJS 5 concatMapTo

by Brian Troncone

HTML

<script src="https://npmcdn.com/@reactivex/[email protected]/dist/global/Rx.umd.js"></script>

JavaScript

//emit value every 2 seconds
const interval = Rx.Observable.interval(2000);
//emit value every second for 5 seconds
const source = Rx.Observable.interval(1000).take(5);
/* 
  ***Be Careful***: In situations like this where the source emits at a faster pace
  than the inner observable completes, memory issues can arise.
  (interval emits every 1 second, basicTimer completes every 5)
*/
//basicTimer will complete after 5 seconds, emitting 0,1,2,3,4
const example = interval
	.concatMapTo(source, 
  	(firstInterval, secondInterval) => `${firstInterval} ${secondInterval}`
   );
/*
  output: 0 0
          0 1
          0 2
          0 3
          0 4
          1 0
          1 1
          continued...
          
*/
const subscribe = example.subscribe(val => console.log(val));