Any need to call unsubscribe for RxJS first()

No. It unsubscribes automatically after calling first(). The current syntax is observable.pipe(first()).subscribe(func); for RxJS 6.

The documentation states:

If called with no arguments, first emits the first value of the source Observable, then completes.

first() will complete after the first item is emitted from the observable.

Also subscribe() takes three arguments, the last one being the complete callback. Running the following code will output 1 followed by 'done'.

Rx.Observable.of(1)
  .subscribe(
  (x) => console.log(x),    // next
  (x) => console.error(x),  // error
  () => console.log('done') // done
)

For the example provided, you dont need to unsubscribe, and neither you need to call first, as Observable.of(1) actually completes after emitting its first (and last) value.