switchMap subscription

a.js

const { rxObserver } = require('api/v0.3');
const { defer, timer, Subject } = require('rxjs');
const { take, switchMap, startWith, endWith, share } = require('rxjs/operators');

// OPEN THE CONSOLE TO SEE SUBSCRIPTION TIMINGS

// defer is called each time it is subscribed to
const source$ = defer(()=>{
  console.log('subscribed at ', Date.now());
  // will emit an event in 10ms
  return timer(10);
})
// UNCOMMENT THIS TO SHARE THE SOURCE
// .pipe(share());


source$.pipe(
  take(1),
  switchMap(value => source$.pipe(
    startWith('>'),
    endWith('<')
  ))
).subscribe(rxObserver('result'));

b.js

const { rxObserver } = require('api/v0.3');
const { defer, timer, Subject } = require('rxjs');
const { take, switchMap, startWith, endWith } = require('rxjs/operators');

// create a hot observable
const hotSource$ = new Subject();
timer(10, 10).pipe(take(5)).subscribe(hotSource$);


// display real source emission
hotSource$.subscribe(rxObserver('real result'));

// and wrapped emission
// as you can see, it omits the first value
hotSource$.pipe(
  take(1),
  switchMap(value => hotSource$.pipe(
    // UNCOMMENT THIS LINE TO GET THE FIRST VALUE
    // startWith(value),
    startWith('>'),
    endWith('<')
  ))
).subscribe(rxObserver('wrapped result'));