Add .flatMapEnd?

We already have .flatMap & .flatMapError, adding .flatMapEnd seems like a logical continuation. It will be a more powerful alternative to .beforeEnd, which allows only to insert a value before end.

Inserting a value before end

// Before
foo.beforeEnd(() => 1)

// After
foo.flatMapEnd(() => Kefir.constant(1))

Inserting a error before end

// Before 
// (will work only if foo does't contain other values, 
// otherwise it will be even trickier)
foo.beforeEnd(() => 1).flatMap(Kefir.constantError)

// After
foo.flatMapEnd(() => Kefir.constantError(1))

Inserting multiple values

// Before 
// (Will work only if foo does't contain other values, 
// otherwise it will be even trickier)
foo.beforeEnd(() => 1).flatMap(() => Kefir.sequentially(1000, [1, 2, 3]))

// After
foo.flatMapEnd(() => Kefir.sequentially(1000, [1, 2, 3]))

Ignoring the end

// Before
foo.ignoreEnd()

// After
// (Suppose we'll have Kefir.neverEnd() 
// similar to Kefir.never() but that also doesn't end)
foo.flatMapEnd(Kefir.neverEnd)

The 1 & 4 examples aren’t very convincing as current alternative is easier, but I still include them to better illustrate potential of .flatMapEnd.

[rpominov]

Maybe something like this:

let bind = () => bindEvents(events, el)

render$$
  .map(render$ => render$.ignoreValues().ignoreErrors().beforeEnd(bind))
  .flatMapLatest()
  .flatMapLatest()

[mAAdhaTTah]

Here’s how I ended up handling it:

function makeEventSwapper(events : EventsConfig, el : HTMLElement) {
    let sub : Subscription = { closed: true };
    // bindEvents returns a stream of DOM events.
    let bind = () => bindEvents(events, el) : Kefir.Observable;

    return (emitter, event) => {
        if (event.type === 'value') {
            if (!sub.closed) {
                sub.unsubscribe();
            }

            const render$ : Kefir.Observable = event.value;
            sub = render$.observe({ complete: () => emitter.next(bind()) });
        }
    };
}

render$$
    .withEventHandler(makeEventSwapper(events, el))
    .flatMapLatest();

Can you see a better way?