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Introduction to FRP
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Stratos Pavlakis
July 21, 2015
Programming
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220
Introduction to FRP
An introduction to Functional Reactive Programming - presented at 9th GreeceJS meetup
Stratos Pavlakis
July 21, 2015
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Transcript
Functional Reactive Programming in Javascript
whoami Stratos Pavlakis Workable UI Tech Lead
[email protected]
th3hunt FRP
newbie!
what’s FRP?
let’s begin with
http://www.reactivemanifesto.org/ Responsive Message Driven Resilient Elastic
sweet dreams
so better start with
reactive paradigm var b = 1, c = 1; var
a = b + c; // a == 2 b = 10; • // a == ? • // imperative paradigm => a == 2 • // reactive paradigm => a == 11
front end development is it synchronous or asynchronous?
• User Input • AJAX • Web Sockets / SSE
• Web Workers • Animations • Cross origin frame communication • Updating the DOM we deal with
• User Input • AJAX • Web Sockets / SSE
• Web Workers • Animations • Cross origin frame communication • Updating the DOM most are async!
tools we use
callbacks var el = document.getElementById("my-button"); el.addEventListener("click", function () { console.log(‘my
button was clicked’); });
promises $http(endpoint1) .get({q: ‘frp’}) .then(function (data) { console.log(‘We got data
back from ajax %s’, data); }) .then(function (data) { return $http(endpoint2).get({id: data.id}); })
generators in ES7 async(function main() { var result1 = await
request( "http://endpoint.1" ); var data = JSON.parse( result1 ); var result2 = await request( "http://endpoint.2?id=" + data.id ); var resp = JSON.parse( result2 ); console.log( "Value: " + resp.value ); })
problems • callback hell • try / catch (except for
generators) • memory leaks • reduced composability
event driven programming we react to events
is reason about event streams what we’re really trying to
do
any number of values Array over any amount of time
f(time) / async an event stream would be
first class citizen of FRP observable
Observer Iterator Gang of Four - Design Patterns ES6 EventEmitter
array VS event
array === collection
events === collection
collections are iterable
observable === collection + time
observable API var subscription = myObservable.subscribe(function (val) { console.log(‘Next: %s’,
val); });
from the EventEmitter? so… how is that different
we know when it’s done var subscription = myObservable.subscribe( onNext,
onError, onCompleted ); like promises
we got set operators • map • flatMap • reduce
• merge • concat • zip
more operators • debounce • buffer • skipUntil • flatMapLatest
• combineLatest • switch • retry
observables can model • mouse clicks • key presses •
scrolling • animations • AJAX Polling, Web Sockets • timers • even… constants
operators http://rxmarbles.com/
filter
debounce
distinctUntilChanged
takeUntil
example please!
mousedown.flatMap((md) => { var startX = md.offsetX, startY = md.offsetY;
return mousemove.map((mm) => { return { left: mm.clientX - startX, top: mm.clientY - startY }; }).takeUntil(mouseup); }).subscribe((pos) => { dragTarget.style.top = pos.top + 'px'; dragTarget.style.left = pos.left + 'px'; }); drag & drop
Autocomplete yes I know, the classic example
requirements • filter queries • throttle requests • retry (overcome
network glitches) • avoid duplicate requests • match results to latest query • abort no longer valid requests
keyup => results var keyPress = $('#search').keyupAsObservable(); .keyPress.map((ev) => {
return ev.target.value; }) .filter((text) => { return text.length > 3; }) .debounce(500) .distinctUntilChanged() .flatMapLatest(search.retry(3).takeUntil(keyPress)) .map((d) => { return d.response[1]; }) .subscribe(showResults, showError); throttling no duplicate requests filtering match/abort response/results
gets even better
things we can do • cancel (can’t do with Promises)
• be lazy until a subscriber subscribes (cold) • setup datasource on first subscription • teardown datasource on disposal
not convinced yet?
observable future • TC39 proposal to add to ES7 ◦
https://github.com/zenparsing/es-observable • Angular 2 first class support • ReactJS first class support
http://victorsavkin.com/post/108837493941/better-support-for-functional-programming-in
Rx in production
still... • steep learning curve • old habits die hard
• tricky to work with classic MV* • poor/difficult documentation (is getting better)
libraries
• Rx.js (port of Reactive Extensions to JS) • Bacon.js
• Kefir (faster bacon :)
origins
Microsoft Research • A Brief Introduction to ActiveVRML - Conan
Elliott • Functional Reactive Animations - Conan Elliott & Paul Hudak
resources • Fran Tutorial - http://conal.net/fran/tutorial.htm • Simply Reactive -
http://conal.net/papers/simply-reactive/ • Reactive Extensions - https://github.com/Reactive-Extensions/RxJS • BaconJS - https://baconjs.github.io/ • Async JavaScript with Reactive Extensions (Jafar Husain) ◦ https://www.youtube.com/watch?v=XRYN2xt11Ek • RxJS at Modern Web UI (Ben Lesh) ◦ https://www.youtube.com/watch?v=yk_6eU3Hcwo • http://www.slideshare.net/stefanmayer13/functional-reactive-programming-with-rxjs • https://gist.github.com/staltz/868e7e9bc2a7b8c1f754 • RxJSKoans - https://rxkoans.codeplex.com/ • RxMarbles - http://rxmarbles.com/ • Reactive programming and MVC (Aaron Stacy) ◦ http://aaronstacy.com/writings/reactive-programming-and-mvc/
None
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