Callbag operator which converts source to a promise containing last emitted value.
import interval from 'callbag-interval'
import pipe from 'callbag-pipe'
import takeUntil from 'callbag-take-until'
import toPromise from 'callbag-to-promise'
pipe(
interval(30),
takeUntil(interval(200)),
toPromise,
).then(value => {
console.log(value) // 5
})