Stopping a Stream with TakeUntil

John Lindquist
InstructorJohn Lindquist

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Observables often need to be stopped before they are completed. This lesson shows how to use takeUntil to stop a running timer. Then we use the starting stream and the stopping stream together to create a simple stopwatch.

Alex Krasnicki
Alex Krasnicki
~ 5 years ago

Hi John!

Great series, thanks!

One question: how would you handle a case when start/stop button is the same button?

Alex.

John Lindquist
John Lindquistinstructor
~ 5 years ago

There's a few different approaches depending on the exact behavior you want. Here's one implementation: https://gist.run/?id=1185b7701932b028401b

Alex Krasnicki
Alex Krasnicki
~ 5 years ago

Amazing! Thank you.

nader dabit
nader dabit
~ 5 years ago

For those of you looking for docs or info about switchMap and switchMapTo, it looks like these were added in version 5.0, they were previously known as flatMapLatest -> https://github.com/ReactiveX/rxjs/blob/master/MIGRATION.md

Julia Passynkova
Julia Passynkova
~ 5 years ago

In the lessen 'Stopping a Stream with TakeUntil' I tried to add error and complete handlers to the subscribe call and on complete function was never called when the stop button is clicked. Any idea why?

John Lindquist
John Lindquistinstructor
~ 5 years ago

@Julia - takeUntil will stop the stream it's attached to, so if you want to complete the start$ stream, you would need to move the takeUntil down:

start$
    .switchMapTo(interval$)
    .takeUntil(stop$)
    .subscribe(
      x=> console.log(x),
      err => console.log(err),
      ()=> console.log('complete')

);

Just be aware you'll no longer be able to click the start button, because the start$ is completed.

Julia Passynkova
Julia Passynkova
~ 5 years ago

Thanks a lot. It works. Reading rxjs documentation it is not obvious what is the "complete" behaviour of each operator, especially when multiple streams are combined. Any suggestions?

Rafael Bitencourt
Rafael Bitencourt
~ 5 years ago

Yep, when I started this video, my idea was to simply chain a takeUntil(stop$) on top of what we already had, something like this:

start$
  .switchMapTo(interval$)
  .takeUntil(stop$)
  .subscribe(x => console.log(x));

So I didn't understand when you did something different. It was when I tried it myself that I realized that the code above will take start$ until stop$, so it only worked once. On this case it's really just the interval$ that we want to takeUntil(stop$).

Really enjoying this @John!

Ming
Ming
~ 4 years ago

Hi Thanks for these series , but I couldn't continue watching it and here is why: Almost all of the series which you are the teacher , starts from somewhere unlcear and ends in somewhere unclear. It looks like you've spent a day discovering , while taking videos and talking, Angular2, rxjs, raact and everything and then at the end you've split them in random episodes and chunks. You don't even say hello at the beginning of the course,. you don't even bother introducing yourself, you always start off a function and keep adding stuff to it. Have a look at this one, you start from absolutely no where without even saying hi, and then you continue with takeUntill without giving any context at all. Generally seems like you don't give a f about the listeners and you just want to finish your work. Almost everytime I hear your voice at the beginning of a series, I just stop watching it because I know I need to go and google every single thing you're using. Could you for the love of JavaScript, at least define your start and ending points. Cheers

ganqqwerty
ganqqwerty
~ 3 years ago

Hi Thanks for these series , but I couldn't continue watching it and here is why: Almost all of the series which you are the teacher , starts from somewhere unlcear and ends in somewhere unclear.

I disagree completely. I bought the subscription precisely because I love John's unique style of no-bullshit explanation of the essence of the topic using only one example. I've never seen anything better. I'm here to learn, and to learn fast, not to listen to teacher's greetings and introductions. If I were John I would even encourage other teachers to do the same, that's what unique about egghead compared to other courses and that's what brought a lot of people here.