multicast

signature: multicast(selector: Function): Observable

Share source utilizing the provided Subject.

Examples

Example 1: multicast with standard Subject

( StackBlitz | jsBin | jsFiddle )

// RxJS v6+
import { Subject, interval } from 'rxjs';
import { take, tap, multicast, mapTo } from 'rxjs/operators';

//emit every 2 seconds, take 5
const source = interval(2000).pipe(take(5));

const example = source.pipe(
  //since we are multicasting below, side effects will be executed once
  tap(() => console.log('Side Effect #1')),
  mapTo('Result!')
);

//subscribe subject to source upon connect()
const multi = example.pipe(multicast(() => new Subject()));
/*
  subscribers will share source
  output:
  "Side Effect #1"
  "Result!"
  "Result!"
  ...
*/
const subscriberOne = multi.subscribe(val => console.log(val));
const subscriberTwo = multi.subscribe(val => console.log(val));
//subscribe subject to source
multi.connect();

Example 2: multicast with ReplaySubject

( StackBlitz | jsBin | jsFiddle )

// RxJS v6+
import { interval, ReplaySubject } from 'rxjs';
import { take, multicast, tap, mapTo } from 'rxjs/operators';

//emit every 2 seconds, take 5
const source = interval(2000).pipe(take(5));

//example with ReplaySubject
const example = source.pipe(
  //since we are multicasting below, side effects will be executed once
  tap(_ => console.log('Side Effect #2')),
  mapTo('Result Two!')
);
//can use any type of subject
const multi = example.pipe(multicast(() => new ReplaySubject(5)));
//subscribe subject to source
multi.connect();

setTimeout(() => {
  /*
   subscriber will receieve all previous values on subscription because
   of ReplaySubject
   */
  const subscriber = multi.subscribe(val => console.group(val));
}, 5000);

Additional Resources

• multicast 📰 - Official docs

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📁 Source Code: https://github.com/ReactiveX/rxjs/blob/master/src/internal/operators/multicast.ts