//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));