Rx.js allows for asynchronous programming using Observables that provide a stream of multiple values over time. The document discusses how Observables can be created from events, combined using operators like map, filter, and flatMap, and subscribed to in order to handle the stream of values. A drag and drop example is provided that creates an Observable stream of mouse drag events by combining mouse down, mouse move, and mouse up event streams. This allows treating the sequence of mouse events as a collection that can be transformed before handling the drag behavior.

1. Rx.js
making async programming simpler

2. 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

3. 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?

4. Asynchronous code

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

6. Sync vs Async dataflow

7. Synchronous dataflow

8. Synchronous dataflow
In

9. Synchronous dataflow
In
1

10. Synchronous dataflow
In
1
2

11. Synchronous dataflow
In
1
2
...

12. Synchronous dataflow
In
1
2
Out
...

13. Asynchronous dataflow
time
Actions

14. Asynchronous dataflow (autocomplete)
time
Actions
keyup

15. Asynchronous dataflow (autocomplete)
time
Actions
keyup
per 2 seconds

16. Asynchronous dataflow (autocomplete)
time
Actions
keyup
per 2 seconds
ajax request

17. Asynchronous dataflow (autocomplete)
time
Actions
keyup
per 2 seconds
ajax request
ajax response

18. Asynchronous dataflow (autocomplete)
time
Actions
keyup
per 2 seconds
ajax request
ajax response
show suggest

19. Asynchronous dataflow (autocomplete)
time
Actions
keyup
per 2 seconds
ajax request
ajax response
show suggest

20. Asynchronous dataflow (autocomplete)
time
Actions
keyup
per 2 seconds
ajax request
ajax response
show suggest
Ooooops

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

22. Callbacks
● Event notification
● Manage control flow

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

24. Callback hell
async_func1(function(err, data){
async_func2(function(err, data){
async_func3(function(err, data){
async_func4(function(err, data){
});
});
});
});

25. Callback hell yeah !!!
async_func1(function(err, data){
if (!err) {
async_func2(function(err, data){
if (!err) {
async_func3(function(err, data){
if (!err) {
async_func4(function(err, data){
});
} else {
log(err);
}
});
} else {
log(err);
}
});
} else {
log(err);
}
});

26. Callback hell yeah !!!
async_func1(function(err, data){
if (!err) {
async_func2(function(err, data){
if (!err) {
async_func3(function(err, data){
if (!err) {
async_func4(function(err, data){
});
} else {
log(err);
}
});
} else {
log(err);
}
});
} else {
log(err);
}
});
UNREADABLE !!!
UNMANAGABLE !!!
UNTESTABLE !!!
UNCOMPOSABLE !!!
PIECE OF ….
CODE

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

29. 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
});
});

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

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

32. How about Promise?

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

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

35. 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.

36. Promise is Observable only with a single value

37. Observable
The Observable object represents a push
based collection.

38. 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) => {}
)

39. 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

40. 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

41. Lazy execution
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}`));
>

42. Observable can be canceled
var source = Rx.Observable.create((observer) => {
var id = setTimeout(() => {
console.log("observable timeout hit");
observer.onNext(25);
}, 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

43. 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
?

44. 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

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

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

47. var dragTarget = document.getElementById('dragTarget');
// Get the three major events collections
var mouseup = Rx.DOM.fromEvent(dragTarget, 'mouseup');
var mousemove = Rx.DOM.fromEvent(document, 'mousemove');
var mousedown = Rx.DOM.fromEvent(dragTarget, 'mousedown');
var mousedrag = mousedown.flatMap(({offsetX, offsetY}) => {
return mousemove
.map(({clientX: x, clientY: y}) => {
return {left: x - offsetX, top: y - offsetY}})
.takeUntil(mouseup)
});
var subscription = mousedrag.subscribe((pos) => {
dragTarget.style.top = pos.top + 'px';
dragTarget.style.left = pos.left + 'px';
});

48. var dragTarget = document.getElementById('dragTarget');
// Get the three major events collections
var mouseup = Rx.DOM.fromEvent(dragTarget, 'mouseup');
var mousemove = Rx.DOM.fromEvent(document, 'mousemove');
var mousedown = Rx.DOM.fromEvent(dragTarget, 'mousedown');
var mousedrag = mousedown.flatMap(({offsetX, offsetY}) => {
return mousemove
.map(({clientX: x, clientY: y}) => {
return {left: x - offsetX, top: y - offsetY}})
.takeUntil(mouseup)
});
var subscription = mousedrag.subscribe((pos) => {
dragTarget.style.top = pos.top + 'px';
dragTarget.style.left = pos.left + 'px';
});
Create observable collections
from DOM events

49. var dragTarget = document.getElementById('dragTarget');
// Get the three major events collections
var mouseup = Rx.DOM.fromEvent(dragTarget, 'mouseup');
var mousemove = Rx.DOM.fromEvent(document, 'mousemove');
var mousedown = Rx.DOM.fromEvent(dragTarget, 'mousedown');
var mousedrag = mousedown.flatMap(({offsetX, offsetY}) => {
return mousemove
.map(({clientX: x, clientY: y}) => {
return {left: x - offsetX, top: y - offsetY}})
.takeUntil(mouseup)
});
var subscription = mousedrag.subscribe((pos) => {
dragTarget.style.top = pos.top + 'px';
dragTarget.style.left = pos.left + 'px';
});
Using power of Rx, combine
existing event streams to produce
mouse drag event collection

50. var dragTarget = document.getElementById('dragTarget');
// Get the three major events collections
var mouseup = Rx.DOM.fromEvent(dragTarget, 'mouseup');
var mousemove = Rx.DOM.fromEvent(document, 'mousemove');
var mousedown = Rx.DOM.fromEvent(dragTarget, 'mousedown');
var mousedrag = mousedown.flatMap(({offsetX, offsetY}) => {
return mousemove
.map(({clientX: x, clientY: y}) => {
return {left: x - offsetX, top: y - offsetY}})
.takeUntil(mouseup)
});
var subscription = mousedrag.subscribe((pos) => {
dragTarget.style.top = pos.top + 'px';
dragTarget.style.left = pos.left + 'px';
});
Subscribe on mouse drag events,
updating top and left attributes

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

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

54. map
http://rxmarbles.com/#map

55. filter
http://rxmarbles.com/#filter

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

57. delay
http://rxmarbles.com/#delay

58. let’s create slow mouse drag
var slow_mousedrag = mousedrag.delay(700)
var subscription = slow_mousedrag.subscribe((pos) => {
dragTarget.style.top = pos.top + 'px';
dragTarget.style.left = pos.left + 'px';
});

59. reduce
http://rxmarbles.com/#reduce

60. 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)

61. flatMap

62. flatMap
var mousedrag = mousedown.flatMap(({offsetX, offsetY}) => {
return mousemove
.map(({clientX: x, clientY: y}) => {
return {left: x - offsetX, top: y - offsetY}})
.takeUntil(mouseup)
});

63. flatMap
var mousedrag = mousedown.flatMap(({offsetX, offsetY}) => {
return mousemove
.map(({clientX: x, clientY: y}) => {
return {left: x - offsetX, top: y - offsetY}})
.takeUntil(mouseup)
});
Outer stream

64. flatMap
var mousedrag = mousedown.flatMap(({offsetX, offsetY}) => {
return mousemove
.map(({clientX: x, clientY: y}) => {
return {left: x - offsetX, top: y - offsetY}})
.takeUntil(mouseup)
});
value as a stream

65. merge
http://rxmarbles.com/#merge

66. 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) => {
dragTarget.style.top = pos.top + 'px';
dragTarget.style.left = pos.left + 'px';
});

67. 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) => {
dragTarget.style.top = pos.top + 'px';
dragTarget.style.left = pos.left + 'px';
});
new stream

68. 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

69. Testing with time machine
Rx.TestScheduler

70. 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)
)

71. 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)
)
stream to test

72. 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)
)
Input stream messages

73. 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)
)
time

74. 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)
)
Expected result at time

75. 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)
)
callback for assert

76. 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

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

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

79. 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

80. 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)
RxReact (simple click count)

81. 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)
RxReact (simple click count)
stream from view for increment and storage
modification

82. 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)
RxReact (simple click count)
merge all streams that can modify UI

83. 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)
RxReact (simple click count)
update UI, making setProps on view
component

84. RxReact (simple click count)
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

85. dispatchActions = (view, eventStream, store) ->
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 ...

86. dispatchActions = (view, eventStream, store) ->
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 ...
decrement click stream

87. dispatchActions = (view, eventStream, store) ->
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 ...
using merge to produce all clicks stream

88. dispatchActions = (view, eventStream, store) ->
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 ...
per 1 second
if clicks counter value changed
sync with server, wait for responce
showsuccesss message

89. dispatchActions = (view, eventStream, store) ->
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 ...
create hide message stream
from previous

90. 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

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

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

93. Thanks : D