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  <title>RxJS Operators</title>
  <script src="https://npmcdn.com/@reactivex/rxjs@5.0.0-beta.4/dist/global/Rx.umd.js"></script>
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//emit value every 2 seconds
const interval = Rx.Observable.interval(2000);
const message = Rx.Observable.of('Second(s) elapsed!');
//when interval emits, subscribe to message until complete, merge for result
const example = interval.concatMapTo(message, (time, msg) => `${time} ${msg}`);
//log values
//output: '0 Second(s) elapsed', '1 Second(s) elapsed'
const subscribe = example.subscribe(val => console.log(val));
//emit value every second for 5 seconds
const basicTimer = Rx.Observable.interval(1000).take(5);
/* 
  ***Be Careful***: In situations like this where the source emits at a faster pace
  than the inner observable completes, memory issues can arise.
  (interval emits every 1 second, basicTimer completes every 5)
*/
//basicTimer will complete after 5 seconds, emitting 0,1,2,3,4
const exampleTwo = interval
    .concatMapTo(basicTimer, 
    (firstInterval, secondInterval) => `${firstInterval} ${secondInterval}`
   );
/*
  output: 0 0
          0 1
          0 2
          0 3
          0 4
          1 0
          1 1
          continued...
          
*/
const subscribeTwo = exampleTwo.subscribe(val => console.log(val));
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