takeUntil - 2

RxJS 5 takeUntil

by Brian Troncone

HTML

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

JavaScript

//emit value every 1s
const source = Rx.Observable.interval(1000);
//is number even?
const isEven = val => val % 2 === 0;
//only allow values that are even
const evenSource = source.filter(isEven);
//keep a running total of the number of even numbers out
const evenNumberCount = evenSource
	.scan((acc, _) => acc + 1, 0);
//do not emit until 5 even numbers have been emitted
const fiveEvenNumbers = evenNumberCount.filter(val => val > 5);
  
const example = evenSource
	//also give me the current even number count for display
  .withLatestFrom(evenNumberCount)
	.map(([val, count]) => `Even number (${count}) : ${val}`)
  //when five even numbers have been emitted, complete source observable
  .takeUntil(fiveEvenNumbers);
/*
	Even number (1) : 0,
    Even number (2) : 2
	Even number (3) : 4
	Even number (4) : 6
	Even number (5) : 8
*/
const subscribe = example.subscribe(val => console.log(val));