Debounce without initial delay

Question

Is there an operator in RxJS that debounces without delaying the "first event in a burst", but delaying (and always emitting) the "last event in a burst"?

Something like this:

---a----b-c-d-----e-f---

after awesome-debounce(2 dashes) becomes:

---a----b------d--e----f

while a normal debounce would be:

-----a---------d-------f

It's kind of a mix between throttle and debounce...

Answer 1

Hmmm, this is the easiest solution I can think of. The interesting part for you is the awesomeDebounce() function that creates the sub-chain.

It basically just combines throttle() and debounceTime() operators:

const Rx = require('rxjs');
const chai = require('chai');

let scheduler = new Rx.TestScheduler((actual, expected) => {
  chai.assert.deepEqual(actual, expected);
  console.log(actual);
});

function awesomeDebounce(source, timeWindow = 1000, scheduler = Rx.Scheduler.async) {
  let shared = source.share();
  let notification = shared
      .switchMap(val => Rx.Observable.of(val).delay(timeWindow, scheduler))
      .publish();

  notification.connect();

  return shared
    .throttle(() => notification)
    .merge(shared.debounceTime(timeWindow, scheduler))
    .distinctUntilChanged();
}

let sourceMarbles =   '---a----b-c-d-----e-f---';
let expectedMarbles = '---a----b------d--e----f';

// Create the test Observable
let observable = scheduler
  .createHotObservable(sourceMarbles)
  .let(source => awesomeDebounce(source, 30, scheduler));

scheduler.expectObservable(observable).toBe(expectedMarbles);
scheduler.flush();

The inner notification Observable is used only for the throttle() operator so I can reset its timer manually when I need. I also had to turn this Observable into "hot" to be independent on the internal subscriptions from throttle().

Answer 2

That's indeed useful debounce type for many situations. Use merge, throttleTime and debounceTime in a next way:

Rx.Observable.merge(source.throttleTime(1000), source.debounceTime(2000))

Full example is here http://jsbin.com/godocuqiwo/edit?js,console

Note: it will emit not only first and last value in debounce interval but also values produced by throttle (which is usually expected and needed, as for scroll debouncing for example).