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“Easier to reason about”

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Reactive programming

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Virtual DOM

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Unidirectional dataflow Functional reactive programming Immutable data structures Virtual DOM One-way data binding Dispatcher Flux Cursors Shadow DOM Components State and props Purity JavaScript in 2015 Declarative Isomorphic

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Golden ratio

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Golden ratio Natural Beautiful Complex

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Equivalent  in JavaScript  UIs?

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What if the user  was a function? @andrestaltz Exploring unidirectional dataflow, MV*,   reactive and functional programming

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No content

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Human Computer

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Interface

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Insight #1: UIs are cycles

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“Output device” “Input device”

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Function f Input Output x f(x)

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Insight #1: UIs are cycles Insight #2: UIs are functions  

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Blocking UIs

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Non-blocking UIs

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js jscon jsconf jsconf budap jsonline  jstor js.com.ph  jsconsole jsconf 2014  jsconf 2015 jsconf budapest Computer

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a•syn•chro•nous adj. Not synchronous; occurring at different times. adj. Allows the other to continue during processing.

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Insight #1: UIs are cycles Insight #2: UIs are functions  Insight #3: UIs are async

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Interface

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Interface Senses Expression

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Expression Senses Expression Senses Symmetry

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Insight #1: UIs are cycles Insight #2: UIs are functions  Insight #3: UIs are async Insight #4: UIs are symmetric

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Output Input Output Input Symmetry

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Input Output

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User Scroll Scroll Scroll Click Scroll Scroll

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Insight #1: UIs are cycles Insight #2: UIs are functions  Insight #3: UIs are async Insight #4: UIs are symmetric Insight #5: The User is a function

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How to code this?

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Computer jsconfbp.com Given URL… …render website.

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[2, 4, 6] ?

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[2, 4, 6] map(x => 10*x) [20, 40, 60]

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[2, 4, 6] filter(x => x < 5) [2, 4]

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map(x&=>&10*x) 2 20 40 60 4 6

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filter(x)=>)x)<)5) 2 2 4 4 6

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time Things happening at certain times

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time Events! Event Stream

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Array: sequence over space. Event Stream: sequence over time.

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delay 2 4 6 8 2 4 6 … ∞

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merge

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window

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combineLatest

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withLatestFrom

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flatMap( )

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Computer jsconfbp.com interactionEvents screenEvents

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function computer(x: EventStream): EventStream { // ... } 1 2 3

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var screenEvents = computer(interactionEvents); screenEvents.listen(function (ev) { ... }); 1 2

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User Scroll Scroll Scroll Click Scroll Scroll interactionEvents screenEvents

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function user(screenEvents: EventStream): EventStream { // one does not simply write this function } 1 2 3

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Scroll Scroll Scroll Click Scroll Scroll interactionEvents screenEvents User

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Scroll Scroll Scroll Click Scroll Scroll interactionEvents screenEvents Screen Eyes DOM Brain Hands DOM Event Dispatcher

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Scroll Scroll Scroll Click Scroll Scroll interactionEvents screenEvents Screen Eyes DOM Brain Hands DOM Event Dispatcher These  are all   we need

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Scroll Scroll Scroll Click Scroll Scroll interactionEvents screenEvents Screen Eyes DOM Brain Hands DOM Event Dispatcher These  are  "remote"

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var interactionEvents = user(screenEvents); interactionEvents.listen(function (ev) { ... }); 1 2

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var screenEvents = computer(interactionEvents);  var interactionEvents = user(screenEvents); 1 2 Equivalent to…

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var a = f(b);  var b = g(a); 1 2

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var a = f(b);  var b = g(a); 1 2

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var b = g(f(b)); 1 Problem!

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var b ← g(f(b)); 1 “=” is assignment! What other types of “=”?

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b = g(f(b))

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Definition: a fixed point of a function f(x)  is a point x0 such that f(x0) = x0. Example: cos(0.73908513…) = 0.73908513…

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Problem: Find screenEvents such that screenEvents = computer(user(screenEvents).

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var screenEvents = computer(interactionEvents);  var interactionEvents = user(screenEvents); 1 2 㱺 interactionsEvents needs to exist   before applying computer() function

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var interactionEvents = makeEmptyEventStream(); var screenEvents = computer(interactionEvents);  var interactionEvents2 = user(screenEvents); 1 2 3 4

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var interactionEvents = makeEmptyEventStream(); var screenEvents = computer(interactionEvents);  var interactionEvents2 = user(screenEvents); 1 2 3 4

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var interactionEvents = makeEmptyEventStream(); var screenEvents = computer(interactionEvents);  var interactionEvents2 = user(screenEvents); 1 2 3 4

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First screen Computer User interactionEvents interactionEvents2 screenEvents

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Computer User interactionEvents interactionEvents2 screenEvents

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Computer User interactionEvents interactionEvents2 screenEvents

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var interactionEvents = makeEmptyEventStream(); var screenEvents = computer(interactionEvents);  var interactionEvents2 = user(screenEvents); interactionEvents2.listen(function (ev) { interactionEvents.emit(ev); }); 1 2 3 4 5 6 7 8

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var interactionEvents = makeEmptyEventStream(); var screenEvents = computer(interactionEvents);  user(screenEvents).listen(function (ev) { interactionEvents.emit(ev); }); 1 2 3 4 5 6

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var interactionEvents = makeEmptyEventStream();   user(computer(interactionEvents))  .listen(function (ev) { interactionEvents.emit(ev); }); 1 2 3 4 5 6 b = g(f(b))

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Solved!

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Computer

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Computer Huge!

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Updates Manipulates Manipulates Sees Uses

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No content

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Model View User ???

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Model View User ??? 01010001010110101 What’s up? ❤

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Model View User ??? Information User language

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Model View User ??? Information User language New information User language

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Model View User Intent Information User language New information User language

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Computer

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Intent View Model or…

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function function or…

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No content

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https://github.com/staltz/cycle Cycle.js Powered by RxJS

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applyToDOM(container, computerFn)  registerCustomElement(tagName, definitionFn) Cycle.js API

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No content

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Cycle.applyToDOM('#app', function computer(interactions) {                       }); 1 2 3 4 5 6 7 8 9  10  11  12  13

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Cycle.applyToDOM('#app', function computer(interactions) {                       }); 1 2 3 4 5 6 7 8 9  10  11  12  13 var changeName$ = interactions.get('.field', 'input') .map(ev => ev.target.value);                  

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Cycle.applyToDOM('#app', function computer(interactions) { var changeName$ = interactions.get('.field', 'input') .map(ev => ev.target.value);                    }); 1 2 3 4 5 6 7 8 9  10  11  12  13   var name$ = changeName$.startWith('');                 

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Cycle.applyToDOM('#app', function computer(interactions) { var changeName$ = interactions.get('.field', 'input') .map(ev => ev.target.value);  var name$ = changeName$.startWith('');                  }); 1 2 3 4 5 6 7 8 9  10  11  12  13     var screen$ = name$.map(name => 

Name

Hello {name}

);   

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Name

Hello {name}

);  return screen$;  }); 1 2 3 4 5 6 7 8 9  10  11  12  13

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Cycle.applyToDOM('#app', function computer(interactions) { return interactions.get('.field', 'input') .map(ev => ev.target.value) .startWith('') .map(name => 

Name

Hello {name}

);  }); 1 2 3 4 5 6 7 8 9  10  11  12 From keyboard… to screen!

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Computer

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Intent View Model

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function intent(interactions) { return interactions.get('.field', 'input')  .map(ev => ev.target.value); } 1 2 3 4

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function model(changeName$) { return Rx.Observable.just('').merge(changeName$); } 1 2 3

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function view(name$) { return name$.map(name => (

Name

Hello {name}

)); } 1 2 3 4 5 6 7 8 9

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function computer(interactions) { return view(model(intent(interactions))); } 1  2  3

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Computer You choose or…

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function function or…

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Intent View Model

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model() view() user() intent()

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model() view() user() intent() name$ screen$ interactions changeName$

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model() view() user() intent() name$ vtree$ interaction$ changeName$ Unidirectional data flow

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[2, 4, 6] map(x => 10*x) [20, 40, 60]

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[2, 4, 6] map(x => 10*x) [20, 40, 60] Functional programming Immutability

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filter(x)=>)x)<)5) 2 2 4 4 6

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filter(x)=>)x)<)5) 2 2 4 4 6 Reactive programming

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function view(name$) { return name$.map(name => (

Name

Hello {name}

)); } 1 2 3 4 5 6 7 8 9

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1 2 3 4 5 6 7 8 9 function view(name$) { return name$.map(name => (

Name

Hello {name}

)); } Virtual DOM

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Insight #1: UIs are cycles Insight #2: UIs are functions  Insight #3: UIs are async Insight #4: UIs are symmetric Insight #5: The User is a function

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Human Computer

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Human Human ?

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Expression Senses Expression Senses

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Expression Senses Expression Senses

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Alice What’s up? Fine! And you?

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What’s up? Good! Fine! And you? Fine! And you? Bob Alice

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merge What’s up? Good! Fine! And you? Fine! And you? What’s up? Good!

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merge What’s up? good! Fine! And you? Fine! And you? What’s up? good! Conversation

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Thank you @andrestaltz