The fourth dimension - An introduction to Functional Reactive Programming

In the spacetime model, the fourth dimension is time. In this talk I show how to transform and manipulate events happening in different moments in time the same way that we transform Arrays or normal sequences, by using the power of Functional Reactive Programming. This will allow us to unite synchronous and asynchronous code, in a way that will help us reason about complex code and build applications that are powerful, reliable and simple to understand.

Transcript

1. The fourth dimension A practical introduction to Functional Reactive Programming by sergi mansilla | @sergimansilla
2. @sergimansilla github.com/sergi
3. Before
5. Shameless linkbaiting
6. Tame your async code with this one weird trick! A practical introduction to Functional Reactive Programming by sergi mansilla | @sergimansilla
7. - Linkbaiting - Time
8. Human beings have hard-wired time in their brain
9. Developers have hard-wired time in their brain (in a slightly different way)
10. 1 CPU Cycle 1 s Level 1 cache access 3 s Level 2 cache access 9 s Level 3 cache access 43 s Main memory access (DRAM, from CPU) 6 min Solid-state disk I/O (flash memory) 2-6 days Rotational disk I/O 1-12 months Internet: San Francisco to Australia 19 years
11. JS developers have hard-wired async in their brain (in a messed up way)
12. Callbacks Promises Generators Events
13. We use events to deal with asynchronous tasks
14. var clicks = 0; document.addEventListener('click', function register(e) { if (clicks < 10) { if (e.clientX > innerWidth / 2) { console.log(e.clientX, e.clientY); clicks += 1; } } else { document.removeEventListener('click', register); } });
15. Why are we still micromanaging code?
16. var clicks = 0; document.addEventListener('click', function register(e) { if (clicks < 10) { if (e.clientX > innerWidth / 2) { console.log(e.clientX, e.clientY); clicks += 1; } } else { document.removeEventListener('click', register); } });
17. var clicks = 0; document.addEventListener('click', function register(e) { if (clicks < 10) { if (e.clientX > innerWidth / 2) { console.log(e.clientX, e.clientY); clicks += 1; } } else { document.removeEventListener('click', register); } });
18. var clicks = 0; document.addEventListener('click', function register(e) { if (clicks < 10) { if (e.clientX > innerWidth / 2) { console.log(e.clientX, e.clientY); clicks += 1; } } else { document.removeEventListener('click', register); } });
19. var clicks = 0; document.addEventListener('click', function register(e) { if (clicks < 10) { if (e.clientX > innerWidth / 2) { console.log(e.clientX, e.clientY); clicks += 1; } } else { document.removeEventListener('click', register); } });
20. var clicks = 0; document.addEventListener('click', function register(e) { if (clicks < 10) { if (e.clientX > innerWidth / 2) { console.log(e.clientX, e.clientY); clicks += 1; } } else { document.removeEventListener('click', register); } });
21. var clicks = 0; document.addEventListener('click', function register(e) { if (clicks < 10) { if (e.clientX > innerWidth / 2 && isAPressed) { console.log(e.clientX, e.clientY); clicks += 1; } } else { document.removeEventListener('click', register); } }); ! var isAPressed = false; document.addEventListener('keydown', e => { isAPressed = e.keyCode === 65; }, false); ! document.addEventListener('keyup', e => { isAPressed = false; }, false);
22. We still code the how instead of the what
23. Programming should be more about the what
25. Declarative
26. Declarative
27. document.addEventListener('keyup', e => { return isAPressed = false; }, false); Void callbacks
28. var clicks = 0; document.addEventListener('click', function register(e) { if (clicks < 10) { if (e.clientX > innerWidth / 2 && isAPressed) { console.log(e.clientX, e.clientY); clicks += 1; } } else { document.removeEventListener('click', register); } }); ! var isAPressed = false; document.addEventListener('keydown', e => { isAPressed = e.keyCode === 65; }, false); ! document.addEventListener('keyup', e => { isAPressed = false; }, false);
29. Climbers
31. State is dangerous
32. Event limbo
33. var clicks = 0; document.addEventListener('click', function register(e) { if (clicks < 10) { if (e.clientX > innerWidth / 2) { console.log(e.clientX, e.clientY); clicks += 1; } } else { document.removeEventListener('click', register); } });
34. Awkward error handling Memory leaks Complex (state)
36. Isn’t that the problem promises try to solve?
37. var y = f(x); var z = g(y); fAsync(x).then(...); gAsync(x).then(...); res = stocks .filter(q => q.symbol == 'FB') .map(q => q.quote) ! res.forEach(x => ... res = stocks //async retrieval .filter(q => q.symbol == 'FB') .map(q => q.quote) ! res.subscribe(x => ... Sync Sync Promises Reactive
38. Click! … … Click! Click!
39. Click! , , Click! Click! [ ]
41. [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] .filter(n => n % 2) .map(n => 'item ' + n) .forEach(n => console.log(n)) ! // "item 1" // "item 3" // "item 5" // "item 7" // "item 9"
42. F R P
43. Final Resting Place
44. Fantasy Role Playing
45. Functional Reactive Programming
48. Deal with values that change over time
49. Alternatives: - Bacon.js - Elm Reactive Extensions for JavaScript
51. RxJS helps us compose asynchronous programs in a declarative way
52. var clicks = 0; document.addEventListener('click', function register(e) { if (clicks < 10) { if (e.clientX > innerWidth / 2) { console.log(e.clientX, e.clientY); clicks += 1; } } else { document.removeEventListener('click', register); } }); Filter Limit to 10 Print the coordinates
53. fromEvent(document, 'click') .filter(c => c.clientX > innerWidth / 2 }) .take(10) .subscribe(c => console.log(c.clientX, c.clientY) })
54. fromEvent(document, 'click') .filter(c => c.clientX > innerWidth / 2 }) .take(10) .subscribe(c => console.log(c.clientX, c.clientY) }) Create Observable
55. fromEvent(document, 'click') .filter(c => c.clientX > innerWidth / 2 }) .take(10) .subscribe(c => console.log(c.clientX, c.clientY) }) Create filtered Observable
 from the first one
56. fromEvent(document, 'click') .filter(c => c.clientX > innerWidth / 2 }) .take(10) .subscribe(c => console.log(c.clientX, c.clientY) }) Create final Observable
 taking only first 10 results
57. fromEvent(document, 'click') .filter(c => c.clientX > innerWidth / 2 }) .take(10) .subscribe(c => console.log(c.clientX, c.clientY) }) Actually kick off computation
58. Observable Observer pattern Iterator pattern
59. Rx.Observer - OnNext() - OnError() - OnComplete()
60. // Creates an observable sequence of 5 integers var source = Rx.Observable.range(1, 5) ! // Prints out each item var subscription = source.subscribe( x => { console.log('onNext: ' + x) }, e => { console.log('onError: ' + e.message) }, () => { console.log('onCompleted') }) ! // => onNext: 1 // => onNext: 2 // => onNext: 3 // => onNext: 4 // => onNext: 5 // => onCompleted
61. var mousemove = fromEvent(document, 'mousemove'); ! var mouseCoords = mousemove.map(e => ({ left: e.clientX, top: e.clientY })) ! var mouseSide = mousemove.map(e => (e.clientX > window.innerWidth / 2 ? 'right' : 'left')) ! mouseCoords.subscribe(pos => coords.innerHTML = pos.top + 'px ' + pos.left + 'px') mouseSide.subscribe(s => side.innerHTML = s); Composability
62. var emsc = Rx.DOM.jsonpRequest({ url: ‘http://seismicportal.eu/?callback=cbfunc...', jsonpCallback: 'cbfunc' }).retry(); ! var usgs = Rx.DOM.jsonpRequest({ url: QUAKE_URL, jsonpCallback: 'eqfeed_callback' }); ! var quakes = Rx.Observable.interval(5000) .flatMap(() => emsc.merge(usgs)) .flatMap(dataset => Rx.Observable.fromArray(dataset.features)) .distinct(quake => quake.code || quake.unid) .subscribe(quake => { var coords = quake.geometry.coordinates; L.circle([coords[1], coords[0]], quake.size).addTo(map); }); Concurrency
64. // Search Wikipedia for a given term function searchWikipedia(term) { var cleanTerm = global.encodeURIComponent(term); var url = ‘/search?q=‘ + cleanTerm + '&cb=JSONPCallback'; return Rx.Observable.getJSONPRequest(url); } ! var input = document.querySelector('#searchtext'), results = document.querySelector('#results'); ! // Get all distinct key up events from the input and var keyup = fromEvent(input, 'keyup') .map(e => e.target.value) .where(text => text.length > 2) // Longer than 2 chars .throttle(200) // Pause for 200ms .distinctUntilChanged(); // Only if the value has changed
65. var searcher = keyup .map(text => searchWikipedia(text)) // Search wikipedia .switchLatest() // Ensure no out of order results .where(data => (data.length === 2)); // Where we have data ! searcher.subscribe(data => { // Append the results (data[1]) }, error => { // Handle any errors });
67. // Search Wikipedia for a given term function searchWikipedia(term) { var cleanTerm = global.encodeURIComponent(term); var url = ‘/search?q=‘ + cleanTerm + '&cb=JSONPCallback'; return Rx.Observable.getJSONPRequest(url); } ! var input = document.querySelector(‘#searchtext'); var results = document.querySelector('#results'); ! // Get all distinct key up events from the input and var keyup = fromEvent(input, 'keyup') .map(e => e.target.value) .where(text => text.length > 2) // Longer than 2 chars .throttle(200) // Pause for 200ms .distinctUntilChanged(); // Only if the value has changed
68. // Search Wikipedia for a given term function searchWikipedia(term) { return fromArray(['JavaScript', 'JavaServer Pages', 'JavaSoft', 'JavaScript library', 'JavaScript Object Notation', 'JavaScript engine', 'JavaScriptCore']); } ! var input = document.querySelector('#searchtext'), results = document.querySelector('#results'); ! // Get all distinct key up events from the input and var keyup = fromEvent(input, 'keyup') .map(e => e.target.value) .where(text => text.length > 2) // Longer than 2 chars .throttle(200) // Pause for 200ms .distinctUntilChanged(); // Only if the value has changed
69. fromArray fromCallback fromEvent fromEventPattern fromIterable fromNodeCallback fromPromise
70. var mouseup = fromEvent(dragTarget, 'mouseup'); var mousemove = fromEvent(document, 'mousemove'); var mousedown = fromEvent(dragTarget, 'mousedown'); ! var mousedrag = mousedown.flatMap(md => { var startX = md.clientX + window.scrollX, startY = md.clientY + window.scrollY, startLeft = parseInt(md.target.style.left, 10) || 0, startTop = parseInt(md.target.style.top, 10) || 0; ! // Calculate delta with mousemove until mouseup return mousemove.map(mm => { mm.preventDefault(); ! return { left: startLeft + mm.clientX - startX, top: startTop + mm.clientY - startY }; }).takeUntil(mouseup); }); ! subscription = mousedrag.subscribe(pos => { dragTarget.style.top = pos.top + 'px'; dragTarget.style.left = pos.left + 'px'; });
71. [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] .filter(n => n % 2) .map(n => 'item ' + n) .forEach(n => console.log(n)) ! // "item 1" // "item 3" // "item 5" // "item 7" // "item 9"
72. [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] .filter(n => n % 2) .map(n => 'item ' + n) .forEach(n => console.log(n)) ! // "item 1" // "item 3" // "item 5" // "item 7" // "item 9" loop loop loop
74. fromArray([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]) .filter(n => n % 2) .map(n => n * 100) .map(n => 'item ' + n) .subscribe(n => console.log(n))
76. First Class async Composability Concurrency Encapsulation Michael Hasselhof sings limbo
77. I am writing a book about this! @sergimansilla
78. Thanks! @sergimansilla