rxjs execute tap only at the first time

Question

I want to execute tap() only when i get the first emitted value

Something like:

Observable
  .pipe(
     tap(() => { /* execute only when I get th         


        

Answer 1

You can share() your main Observable like below:

import { timer, of, BehaviorSubject, interval } from 'rxjs';
import { tap, mapTo, share, shareReplay, } from 'rxjs/operators';

const source$ = timer(1000)
.pipe(
  tap((v) => console.log('SIDE EFFECT')),
  mapTo('RESULT')
)
const sharedSource$ = source$.pipe(share());
// or shareReplay(1) if you want to ensure every subscriber get the last value event if they will subscribe later;

sharedSource$.subscribe(console.log);
sharedSource$.subscribe(console.log);
sharedSource$.subscribe(console.log);
sharedSource$.subscribe(console.log);
sharedSource$.subscribe(console.log);
sharedSource$.subscribe(console.log);
sharedSource$.subscribe(console.log);

https://stackblitz.com/edit/typescript-qpnbkm?embed=1&file=index.ts

This is an example like in learn-rxjs