// RxJS v6+
import { interval, timer } from 'rxjs';
import { takeUntil } from 'rxjs/operators';
​
//emit value every 1s
const source = interval(1000);
//after 5 seconds, emit value
const timer$ = timer(5000);
//when timer emits after 5s, complete source
const example = source.pipe(takeUntil(timer$));
//output: 0,1,2,3
const subscribe = example.subscribe(val => console.log(val));

// RxJS v6+
import { interval } from 'rxjs/observable/interval';
import { takeUntil, filter, scan, map, withLatestFrom } from 'rxjs/operators';
​
//emit value every 1s
const source = interval(1000);
//is number even?
const isEven = val => val % 2 === 0;
//only allow values that are even
const evenSource = source.pipe(filter(isEven));
//keep a running total of the number of even numbers out
const evenNumberCount = evenSource.pipe(scan((acc, _) => acc + 1, 0));
//do not emit until 5 even numbers have been emitted
const fiveEvenNumbers = evenNumberCount.pipe(filter(val => val > 5));
​
const example = evenSource.pipe(
  //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));

// RxJS v6+
import { fromEvent } from 'rxjs';
import { takeUntil, mergeMap, map } from 'rxjs/operators';
​
const mousedown$ = fromEvent(document, 'mousedown');
const mouseup$ = fromEvent(document, 'mouseup');
const mousemove$ = fromEvent(document, 'mousemove');
​
// after mousedown, take position until mouse up
mousedown$
  .pipe(
    mergeMap(_ => {
      return mousemove$.pipe(
        map((e: any) => ({
          x: e.clientX,
          y: e.clientY
        })),
        // complete inner observable on mouseup event
        takeUntil(mouseup$)
      );
    })
  )
  .subscribe(console.log);