staltz/xstream

An extremely intuitive, small, and fast functional reactive stream library for JavaScript

Sudarsan Balaji

@artfuldev

I wanna create a diff stream with time between its events. How do I do that?

const source$ = xs.fromArray([[1,2],[1],[1,2,3,4,5]]);
const required$ =
  source$
    .startWith([])
    . // what should I do here, to get
      // -[]--[1]--[1,2]--[1]--[1,2]--[1,2,3]--[1,2,3,4]--[1,2,3,4,5]-|

The -- is constant time between the diff events

trying to modify a list of items slowly (one-by-one) even though I get all of them at a time

Michael Maier

@maiermic

how can I duplicate the first element of a stream?

Michael Maier

@maiermic

well it seems I have another issue
at least Stream.merge(elements$, elements$.take(1)) is working

this example works as expected

const xs = xstream.Stream

var stream = xs.periodic(1000).take(3)

xs.merge(stream, stream.take(1))
  .addListener({
    next: i => console.log(i),
    error: err => console.error(err),
    complete: () => console.log('completed'),
  })

Output:

0
0
1
2
"completed"

Michael Maier

@maiermic

if I add a debug to stream I get unexpected output

var stream = xs.periodic(1000).take(3).debug('test')

Output:

"test:"
0
0
0
"test:"
1
1
"test:"
2
2
"completed"

bug or feature?

Steve Lee

@SteveALee

seems good to me. Why would it be a bug? Is printing your 'test' label and then the value - all be it on separate lines.

Michael Maier

@maiermic

I expect

"test:"
0
0
"test:"
1
"test:"
2
"completed"

oh, this might be a misunderstanding of mine caused by JSBin

it's console prints

"test:"
0

instead of

test: 0

Steve Lee

@SteveALee

Yeah, that was my point. I wondered why was on separate line - so it's JSBin!

Alex

@whitecolor

@staltz is it correct that operators convert MemoryStream to Stream?

André Staltz

@staltz

@whitecolor some of them do, like filter, because filter "removes" events and unless we buffer all events from the past, we cant guarantee that the output stream after filter would remain as a memorystream

Alex

@whitecolor

I think this should be stated in docs

Michal Vanko

@michalvankodev

Hello, I'm reading documentation for flattenSequentially

I think the Marble diagram is bit misleading.

* In essence, `flattenSequentially` concatenates all nested streams.
 *
 * Marble diagram:
 *
 * ```text
 * --+--------+-------------------------
 *   \        \
 *    \       ----1----2---3--|
 *    --a--b----c----d--|
 *          flattenSequentially
 * -----a--b----c----d------1----2---3--
 *

```

Shouldn't it be

 * --+--------+-------------------------
 *   \        \
 *    \       ----1----2---3--|
 *    --a--b----c----d--|
 *          flattenSequentially
 * -----a--b----c----d--1-2-3-----

Basically the events which were buffered shouldn't they be emmited right away?

Alex

@whitecolor

why? just after first streams completes it will subscribe to the second and emit the values

Michal Vanko

@michalvankodev

But those buffered events shouldn't be postponed by the time it took them to be emmited in the original stream

Alex

@whitecolor

it will not buffer, it will just subscribe, the example assumes that second stream has no subscribers yet

if it is started you would probably seen only 3 and if its memory stream 2 and 3

I believe it is so in theory) check it in pracice

Michal Vanko

@michalvankodev

Yea.. There is no documentation about subscribing to that second stream.

Alex

@whitecolor

Well the thing is that flattenConcurrenlty will subscribe to second stream as soon as arrives, and flattenSequentially only after previous stream completes

Michal Vanko

@michalvankodev

I get this.. I'm just concerned about the time which it takes to emit the values.

Alex

@whitecolor

say first stream is periodic(1000).take(4) and second periodic(5000).take(3) first start and emits abc, second arrives but will not be subscribed (no emittion) after 4 second, it will be subscribed and will emit 3 values in 15 seconds

you should consider hot/cold/multicasted and meta streams conceptions

it is simple

Michal Vanko

@michalvankodev

I'm going to try this out ;)

Alex

@whitecolor

on this diagram secons + is a moment of arrival of second stream to metastream, not the time of subscribtion

Michal Vanko

@michalvankodev

It dropped all of the values emitted before.. there is no buffer for those

Alex

@whitecolor

if your second stream had subscribers before

Michal Vanko

@michalvankodev

yes ;)

André Staltz

@staltz

Yes this is a tricky thing, and also occurs with concatMap in RxJS, it depends whether the thing being concatted is hot or cold

the intuition is not exactly "concatenation of values", it's more about "sequential subscription to different streams"

that's why I like "flattenSequentially" as a name

Michal Vanko

@michalvankodev

Wise choice :) .. Yesterday I got a question from my colleague if something like what I asked for is possible.. to deal with the events in order would be possible via some operator.. I can only think of flattenConcurrently with some extra logic to delay events from streams that are emitted before the first one finishes

André Staltz

@staltz

probably requires some buffering, we haven't yet made buffer or toArray in xstream, but I think it's on the to-do list

Michal Vanko

@michalvankodev

Didn't something with mapTo() changed in xtream@11? I was generating new IDs with mapTo and the function I've mapped to was always called before I've updated dependencies the last time. Now that function is only called once

Nick Johnstone

@Widdershin

@michalvankodev can you share a code sample?

is it stream$.mapTo(generateId())?

Michal Vanko

@michalvankodev

yes exactly

I get it that it shouldn't work.. .But it worked before

Nick Johnstone

@Widdershin

 λ cat > test.js
const xs = require('xstream').default;

xs.of(1, 2, 3).mapTo(Math.random()).addListener({next: console.log})

 λ npx -p xstream@10 node test.js
npx: installed 2 in 2.063s
0.5104117713843652
0.5104117713843652
0.5104117713843652

 λ npx -p xstream@11 node test.js 
npx: installed 2 in 2.463s
0.07187050076072277
0.07187050076072277
0.07187050076072277

From what I understand, it wouldn't be possible for xstream to change this behaviour

Where communities thrive

People

Repo info

Activity