Rxjs kyivjs 2015

Rx.js
making async programming simpler

About me
Mostovenko Alexander
Python developer at
Writing mostly in python and coffeescript.
Love FP stuff.
Traveling, snowboarding, cycling.
https://twitter.com/MostovenkoA
https://github.com/AlexMost

Why Rx.js and not another FRP lib?
● Implemented in a lot of languages
(.NET, Java, Ruby, Python, Clojure, Scala,
Haskell, Objective-C).
● Has a huge amount of docs and examples.
● Why not?

Async code in javascript
● Some computation with delayed result.
(data fetch, animations, DOM operations)
● Reacting to events (event handlers)

Synchronous dataflow
In
1
2
...

Synchronous dataflow
In
1
2
Out
...

Asynchronous dataflow
time
Actions

Asynchronous dataflow (autocomplete)
time
Actions
keyup

time
Actions
keyup
per 2 seconds

time
Actions
keyup
per 2 seconds
ajax request

time
Actions
keyup
per 2 seconds
ajax request
ajax response

time
Actions
keyup
per 2 seconds
ajax request
ajax response
show suggest

time
Actions
keyup
per 2 seconds
ajax request
ajax response
show suggest
Ooooops

Problems with async code
1. How to manage async flow in code?
2. How to handle errors?
3. How to compose?

Callbacks
● Event notification
● Manage control flow

Callbacks
● Event notification - Yes
● Manage control flow - Nooooooooooo

Callback hell
async_func1(function(err, data){
});
});
});
});

Callback hell yeah !!!
if (!err) {
if (!err) {
if (!err) {
});
} else {
log(err);
}
});
} else {
log(err);
}
});
} else {
log(err);
}
});

Callback hell yeah !!!
if (!err) {
if (!err) {
if (!err) {
});
} else {
log(err);
}
});
} else {
log(err);
}
});
} else {
log(err);
}
});
UNREADABLE !!!
UNMANAGABLE !!!
UNTESTABLE !!!
UNCOMPOSABLE !!!
PIECE OF ….
CODE

Monad
A monad is just a monoid in the category of
endofunctors

Callback vs Black hole
some_async_func(function(err, result) {
// ... looks like we are in trap
another_wonderful_func(function(err, result){
// ... you are in trap
});
});

Callback vs Black Hole
1. No return value (undefined)

Callback vs Black Hole
1. No return value (undefined)
2. One way ticket (callback hell)

Promise
var promise = new Promise((resolve, reject) => {
// ... some async staff
});
promise.then(
(result) => {},
(error) => {}
)

Promise
1. Step forward from callbacks for control flow
managing
2. Error handling

Why we should look at Observable?
1. Promise represents only single value.
2. How to cancel?
3. Lazy execution.
4. We can work with Observable as easy as with
promise.

Promise is Observable only with a single value

Observable
The Observable object represents a push
based collection.

Observable
var source = Rx.Observable.create((observer) =>
// some async operation
observer.onNext(data)
// or ..
observer.onError(data)
// or ..
observer.onCompleted(data)
);
source.subscribe(
(data) => {}
(err) => {}
)

Observlable vs promise example
var source = Rx.Observable.create((observer) => {
setTimeout(() => {
console.log("observable timeout hit");
observer.onNext(25);
}, 500);
console.log('observable started')});
source.subscribe(x => console.log(`observable value ${x}`));
Observable
> observable started
> observable timeout hit
> observable value 25

Observlable vs promise example
var promise = new Promise((resolve) => {
setTimeout(() => {
console.log("promise timeout hit");
resolve(25);
}, 500);
console.log("promise started");});
promise.then(x => console.log(`promise value ${x}`));
Promise
> promise started
> promise timeout hit
> promise value 25

Lazy execution
setTimeout(() => {
}, 500);
console.log('observable started')});
// source.subscribe(x => console.log(`observable value ${x}`));
>

Observable can be canceled
var id = setTimeout(() => {
}, 500);
console.log('observable started');
return () => {
console.log("dispose called")
clearTimeout(id);}
});
var disposable = source.subscribe(
x => console.log(`observable value ${x}`));
setTimeout(() => disposable.dispose(), 100)
> observable started
> dispose called

Asynchronous programming landscape
multiple
values
single
value
sync async
a = f(x) a = f(x).then(...)
collection = [1, 2, 3]
a = collection
.filter((v) => v > 2)
Promise
Array
Sync value
?

Asynchronous programming landscape
multiple
values
single
value
sync async
a = f(x) a = f(x).then(...)
collection = [1, 2, 3]
a = collection
.filter((v) => v > 2)
move = Rx.Observable.fromEvent(document, 'mousemove')
my_moves = move
.filter((ev) => ev.clientX > 100)
my_moves.subscribe(...)
Promise
Array
value
Observable

How to create Observable
● Observable.create
● Observable.fromEvent
● Observable.fromNodeCallback
● Observable.fromArray
● Observable.fromPromise

Drag & Drop example
What if i told you ….
That mouse move event is an array and you
can map, filter over it?

return mousemove
.takeUntil(mouseup)
});
});
Create observable collections
from DOM events

return mousemove
.takeUntil(mouseup)
});
});
Using power of Rx, combine
existing event streams to produce
mouse drag event collection

return mousemove
.takeUntil(mouseup)
});
});
Subscribe on mouse drag events,
updating top and left attributes

Observable are first class events
Can be:
- passed as a parameter
- returned from a function
- assigned to a variable

Some common basic operations
map
filter
reduce
zip
merge
flatMap
...
https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/observable.md

filter
http://rxmarbles.com/#filter

var mousedrag_in_area = mousedrag.filter(({top, left}) => {
return top <= 200 && left <= 200
});
var subscription = mousedrag_in_area.subscribe((pos) => {
});
let’s filter drag area

delay
http://rxmarbles.com/#delay

let’s create slow mouse drag
var slow_mousedrag = mousedrag.delay(700)
var subscription = slow_mousedrag.subscribe((pos) => {
});

reduce
http://rxmarbles.com/#reduce

let’s record our drag path
var drag_path = mousedrag
.takeUntil(mouseup)
.reduce(((a, b) => a + `${b.top} ${b.left};`), "")
drag_path.subscribe((path) => pathTarget.innerHTML = path)

flatMap
return mousemove
.takeUntil(mouseup)
});

flatMap
return mousemove
.takeUntil(mouseup)
});
Outer stream

flatMap
return mousemove
.takeUntil(mouseup)
});
value as a stream

merge
http://rxmarbles.com/#merge

merge
var btnTarget = document.getElementById('okbtn');
var buttonClicks = Rx.DOM.fromEvent(btnTarget, 'click');
var move_to_100 = buttonClicks.map(() => {return {left: 100, top: 100}});
var change_position = Rx.Observable.merge(mousedrag, move_to_100)
change_position.subscribe((pos) => {
});

merge
var btnTarget = document.getElementById('okbtn');
var buttonClicks = Rx.DOM.fromEvent(btnTarget, 'click');
var move_to_100 = buttonClicks.map(() => {return {left: 100, top: 100}});
var change_position = Rx.Observable.merge(mousedrag, move_to_100)
change_position.subscribe((pos) => {
});
new stream

And a lot of other methods ….
● amb
● and
● asObservable
● average
● buffer
● bufferWithCount
● bufferWithTime
● bufferWithTimeOrCount
● catch | catchError
● combineLatest
● concat
● concatAll
● concatMap
● concatMapObserver
● connect
● includes
● controlled
● count
● debounce
● debounceWithSelector
● defaultIfEmpty
● delay
● delaySubscription
● delayWithSelector
● dematerialize
● distinct
● distinctUntilChanged
● do
● doOnNext
● doOnError
● doOnCompleted
● doWhile
● elementAt
● elementAtOrDefault
● every
● expand
● extend
● filter
● find
● findIndex
● first
● firstOrDefault
● flatMap
● flatMapObserver
● flatMapLatest
● forkJoin
● groupBy
● groupByUntil
● groupJoin
● ignoreElements
● indexOf
● isEmpty
● join
● jortSort
● jortSortUntil
● last
● lastOrDefault
● merge
● mergeAll
● min
● minBy
● multicast
● observeOn
● onErrorResumeNext
● pairwise
● partition
● pausable
● pausableBuffered
● pluck
● publish
● publishLast
● publishValue
● share
● shareReplay
● shareValue
● refCount
● reduce
● repeat
● replay
● retry
● retryWhen
● sample
● scan
● select
● selectConcat
● selectConcatObserver
● selectMany
● selectManyObserver
● selectSwitch
● sequenceEqual
● single
● singleOrDefault
● singleInstance
● skip
● skipLast
● skipLastWithTime
● skipUntil
https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/observable.md

Testing with time machine
Rx.TestScheduler

var mult_stream = some_stream.debounce(100).map((n) => n * 2)
assertRxActions(
mult_stream,
[
[100, {value: 20}],
[200, {value: 40}]
],
[
[200, {value: 80}]
],
(result) => assertTrue(result)
)

assertRxActions(
mult_stream,
[
[100, {value: 20}],
[200, {value: 40}]
],
[
[200, {value: 80}]
],
)
stream to test

assertRxActions(
mult_stream,
[
[100, {value: 20}],
[200, {value: 40}]
],
[
[200, {value: 80}]
],
)
Input stream messages

assertRxActions(
mult_stream,
[
[100, {value: 20}],
[200, {value: 40}]
],
[
[200, {value: 80}]
],
)
time

assertRxActions(
mult_stream,
[
[100, {value: 20}],
[200, {value: 40}]
],
[
[200, {value: 80}]
],
)
Expected result at time

assertRxActions(
mult_stream,
[
[100, {value: 20}],
[200, {value: 40}]
],
[
[200, {value: 80}]
],
)
callback for assert

React ?
● Rx-React
● RxReact
● cycle-react
● React RxJS Autocomplete
● React RxJS TODO MVC
● Rx TODO MVC
● React RxJS Router
● React + RxJS + Angular 2.0 di.js TODO MVC
● React + RxJS Reactive Cube
● Real-Time with React + RxJS + Meteor
● React + RxJS Flow
● Reactive Widgets
● React RxJS Infinite Scroll

Flux ?
● Rx-Flux
● ReactiveFlux
● Thundercats.js
● Flurx
● RR

RxReact
some info - http://habrahabr.ru/post/251835/
repo with demos - https://github.com/AlexMost/RxReact

RxReact (simple click count)
Simple case
demo - http://alexmost.github.io/RxReact/hello_world/public/index.html
code - https://github.com/AlexMost/RxReact/tree/master/hello_world/hello_world

dispatchActions = (view, eventStream, store) ->
incrementClickStream = eventStream
.filter(({action}) -> action is "increment_click_count")
.do(-> store.incrementClicksCount())
Rx.Observable.merge(
incrementClickStream
# some more actions here for updating view ...
).subscribe(
-> view.setProps getViewState(store)
(err) ->
console.error? err)

).subscribe(
(err) ->
console.error? err)
stream from view for increment and storage
modification

).subscribe(
(err) ->
console.error? err)
merge all streams that can modify UI

).subscribe(
(err) ->
console.error? err)
update UI, making setProps on view
component

More complex case
1. Decrement.
2. Sync with server (per 1 second).
3. Sync only if value changed.
4. Show sync success message.
5. Hide success message after 2 seconds.
demo - http://alexmost.github.io/RxReact/hello_world2/public/index.html
code - https://github.com/AlexMost/RxReact/tree/master/hello_world2/hello_world2

incrementClickStream = ...
decrementClickStream = eventStream
.filter(({action}) -> action is "decrement_click_count")
.do(-> store.decrementClickscount())
.share()
countClicksStream = Rx.Observable
.merge(incrementClickStream, decrementClickStream)
showSavedMessageStream = countClicksStream
.throttle(1000)
.distinct(-> store.getClicksCount())
.flatMap(-> saveToDb store.getClicksCount())
.do(-> store.enableSavedMessage())
hideSavedMessageStream = showSavedMessageStream.delay(2000)
.do(-> store.disableSavedMessage())
// merge ...

.share()
.throttle(1000)
// merge ...
decrement click stream

.share()
.throttle(1000)
// merge ...
using merge to produce all clicks stream

.share()
.throttle(1000)
// merge ...
per 1 second
if clicks counter value changed
sync with server, wait for responce
showsuccesss message

.share()
.throttle(1000)
// merge ...
create hide message stream
from previous

Conclusion
● Rx is a powerful tool for writing async code
● Helps to write modular and composable code
● Solves a lot of hard testing problems
● Solves problem of error handling and resource
management

Resources
http://rxmarbles.com/
http://jaredforsyth.com/rxvision/
https://github.com/jhusain/learnrx

Talk demos here
https://github.com/AlexMost/kyivjs_2015

Rxjs kyivjs 2015

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