RxJS share() Multicasting Operator

RxJS share() operator is a multicasting operator which returns a new observable that shares or multicasts the original observable. As long as there is at least one subscriber, this observable will be subscribed and emitting data. When all subscribers have unsubscribed, it will unsubscribe from the source observable. Because the observable is multicasting, it makes the stream hot. This is an alias for multicast(() => new Subject()), refCount().

Syntax:

Following is the syntax of the RxJS share() multicasting operator:

Parameter Explanation

There is no such parameter that we have to explain.

Return value

The RxJS share() operator returns observable causes the source observable to emit items to its observers when the connection is established.

Let us see some examples of the RxJS share() operator to understand it clearly.

Example 1

import { interval} from 'rxjs';
import { take, share} from 'rxjs/operators';
let observer = interval(1000).pipe(take(5), share());
const subscribe_one = observer.subscribe(
   x => console.log("Value from Sub1 = "+x)
);
const subscribe_two = observer.subscribe(
   x => console.log("Value from Sub2 = "+x)
);
setTimeout(() => {
   const subscribe_three = observer.subscribe(
      x => console.log("Value from Sub3 = "+x)
   );
}, 2000);

Output:

After executing the above example, you will see the following result:

Example 2 (Multiple subscribers sharing source)

import { timer } from 'rxjs';
import { tap, mapTo, share } from 'rxjs/operators';
//emit value in 1s
const source = timer(1000);
//log side effect, emit result
const example = source.pipe(
  tap(() => console.log('***SIDE EFFECT***')),
  mapTo('***RESULT***')
);
const subscribe = example.subscribe(val => console.log(val));
const subscribeTwo = example.subscribe(val => console.log(val));
//share observable among subscribers
const sharedExample = example.pipe(share());
const subscribeThree = sharedExample.subscribe(val => console.log(val));
const subscribeFour = sharedExample.subscribe(val => console.log(val));

Output:

After executing the above example, you will see the following result: