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Bending time with RxJS A practical introduction to Reactive Extensions by sergi mansilla | @sergimansilla Reactive Amsterdam, 2nd December 2015

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@sergimansilla

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http://github.com/sergi

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Previously

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https://pragprog.com/book/smreactjs/reactive-programming-with-rxjs

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Human beings have hard-wired time in their brain

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async / sync

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Callbacks Promises Generators Events

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Concurrency is hard

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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); } });

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Why are we still micromanaging code? Um yeah…about these event callbacks

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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); } });

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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); } });

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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); } });

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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); } });

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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);

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We code the how instead of the what

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Programming should be about the what

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State is dangerous

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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);

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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); } }); Where is my handler??

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Event limbo

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Isn’t that the problem promises try to solve?

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var y = f(x); var z = g(y); fAsync(x).then(...); gAsync(y).then(...); res = stocks // array .filter(q => q.symbol == 'FB') .map(q => q.quote) res.forEach(x => ... res = stocks // async anything .filter(q => q.symbol == 'FB') .map(q => q.quote) res.subscribe(x => ... Sync Sync Promises RxJS

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Click! … … Click! Click!

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Click! , , Click! Click! [ ]

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[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"

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Reactive Programming

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Deal with values that change over time

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RxJS helps us compose asynchronous and event-based programs

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The Observable a universal datatype?

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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

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fromEvent(document, 'click') .filter(c => c.clientX > innerWidth / 2 }) .take(10) .subscribe(c => console.log(c.clientX, c.clientY) })

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fromEvent(document, 'click') .filter(c => c.clientX > innerWidth / 2 }) .take(10) .subscribe(c => console.log(c.clientX, c.clientY) }) Create Observable

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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

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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

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fromEvent(document, 'click') .filter(c => c.clientX > innerWidth / 2 }) .take(10) .subscribe(c => console.log(c.clientX, c.clientY) }) Actually kick off computation

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First class async (Holy sh*t!)

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Observable Observer pattern Iterator pattern

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Rx.Observable - OnNext() - OnError() - OnComplete()

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// 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

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function getDrag(el) { return Dom.mousedown(el) .flatMap(md => Dom.mousemove(document)) .takeUntil(Dom.mouseup(document)); } getDrag() .subscribe(e => log(e.clientX, e.clientY));

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// Search Wikipedia for a given term function searchWikipedia(term) { var cleanTerm = global.encodeURIComponent(term); var url = 'http://en.wikipedia.org/w/api.php?...'; return Rx.Observable.getJSONPRequest(url); } // 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 var doSearch = keyup .flatMap(text => searchWikipedia(text)) // Search wikipedia .switch() // Ensure no out of order results doSearch.subscribe(results => { // Do stuff with the results! });

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No external state

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// Search Wikipedia for a given term function searchWikipedia(term) { return fromArray(['JavaScript', 'JavaServer Pages', 'JavaSoft', 'JavaScript library', 'JavaScript Object Notation', 'JavaScript engine', 'JavaScriptCore']); } // 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

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filter { }

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map { } 1 2 3 4 5 1 4 6 8 10

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0 1 merge 1 0 0 1 A B C 3 2 0 1 3 2 100ms 200ms

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throttleFirst(300) 1 2 3 1 3 300ms 4 5 6 300ms 7 7

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Flat A A 1 A 2 A 3 FlatMap

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fromArray fromCallback fromEvent fromEventPattern fromIterable fromNodeCallback fromPromise

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[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"

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[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

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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))

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Only scratching the surface

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Only scratching the surface Schedulers Async testing
 Libraries

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/** @jsx hJSX */ import Cycle from '@cycle/core'; import {makeDOMDriver, hJSX} from '@cycle/dom'; function main(drivers) { return { DOM: drivers.DOM.select('input').events('click') .map(ev => ev.target.checked) .startWith(false) .map(toggled =>
Toggle me

{toggled ? 'ON' : 'off'}

) }; } let drivers = { DOM: makeDOMDriver('#app') }; Cycle.run(main, drivers);

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https://pragprog.com/book/smreactjs/reactive-programming-with-rxjs

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Thanks! @sergimansilla