rxjs6 - toPromise doesn't return last observed value

Question

Here is an example that can be run with ts-node. Why is the value displayed in result 2 instead of 3.

import { interval, Subject } from 'rxjs';
import { startWith, takeUntil, tap, map } from 'rxjs/operators';

const done = new Subject();
let times = 0;

function test() {
  return interval(5000).pipe(
    startWith(0),
    map(() => times++ ),
    tap(n => {
      console.log(n);
      if (n === 3) {
        done.next();
      }
    }),
    takeUntil(done),
  ).toPromise();
}

test().then(n => {
  console.log('result: ', n);
}).catch(err => {
  console.error('error: ', err.message);
});

output is: what expecting result: 3

0
1
2
3
result:  2

question from:https://stackoverflow.com/questions/65834915/topromise-doesnt-return-last-observed-value

Answer 1

Waitting for answers