RxJS -如何使可观察流仅在第一次订阅时触发

import { of } from 'rxjs';
import { shareReplay } from 'rxjs/operators';

const observable = of(1, 2, 3).pipe(
  shareReplay()
);

observable.subscribe(value => {
  console.log('First subscription:', value);
});

observable.subscribe(value => {
  console.log('Second subscription:', value);
});

First subscription: 1
First subscription: 2
First subscription: 3
Second subscription: 1
Second subscription: 2
Second subscription: 3