delayWhen operator doesn't delay the events if delayDurationSelector returns a Subject.

[EarthyOrange]

Bug Report

Current Behavior
The delayWhen operator doesn't delay the events if delayDurationSelector returns a Subject.

Reproduction

• https://stackblitz.com/edit/rxjs-qzqjvf

Expected behavior
In the reproducible example, values 1-4 should not be printed.

Environment

• RxJS version: ^6.5.1

[cartant]

It's because the subject - that you are using as the notifier - completes. The implementation of delayWhen does not delay if the notifier completes. There is some discussion here relating to this.

I've edited that issue's title to better reflect the problem. Fixing this bug will be a breaking change that we can introduce in version 7.

[cartant]

Closing this as a dupe of #3665, as I've had a play with the repro and if the take - that's applied to the observable to which the subject is subscribed - is bumped to, say, 100, the delay is applied. So this is the same problem as in the above issue - the subject completes when the take completes its source.

[EarthyOrange]

Thank you for looking in to it so quickly!!